Controlled synthesis of noble metal nanocrystals has received enormous attention due to the ability of tailoring the properties of nanocrystals by tuning their shape, size, and composition. The seed-mediated growth method is one of the most reliable and versatile methods to control the shapes of noble metal nanocrystals. This feature article highlights recent strategies regarding shape-controlled synthesis of noble metal nanocrystals by the seed-mediated growth method, with the aim of introducing new strategies and offering new mechanistic insights into nanocrystal shape evolution. Critical parameters affecting the nucleation and growth of noble metal NCs are systemically introduced and analyzed. New developments of extended seed-mediated growth methods were also introduced. Finally, the perspectives of future research on the seed-mediated growth method are also discussed.

Tetrahexahedral, polyhedral, and branched Pd@Au core–shell nanostructures were selectively produced by manipulating their growth thermodynamics and kinetics. The current density in the electrochemical oxidation of H2O2 and the electrochemiluminescence density of luminol–H2O2 systems at the tetrahexahedron modified electrode are 43.5 and 16.4 times that at the bulk Au electrode, respectively.

Both the electrochemiluminescence (ECL) method for sensitive detection of ozone and the ECL resonance energy transfer (ECRET) using ozone have been reported for the first time. It is based on the ECRET of Ru(phen)32+-doped silica nanoparticles (RuSiNPs) to indigo carmine. In the absence of ozone, the ECL of RuSiNPs is quenched as a result of the ECRET of RuSiNPs to indigo carmine. In the presence of ozone, the ECL of the system is “turned on” because ozone can oxidize indigo carmine and interrupt the ECRET from RuSiNPs to indigo carmine. In this way, it provides a simple ECL sensing of ozone via the proposed RuSiNP-based ECRET strategy with a linear range from 0.05–3.0 μM and a limit of detection (LOD) of 30 nM. The detection takes less than 5 min. This method is also successfully applied in the analysis of ozone in human serum samples and atmospheric samples.

Copper nanoclusters (Cu NCs) are found to possess intrinsic peroxidase-like activity for the first time. Similar to nature peroxidase, they can catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine by H2O2 to produce a nice blue color reaction. Compared with horseradish peroxidase, Cu NCs exhibits higher activity near neutral pH, which is beneficial for biological applications. The increase in absorbance caused by the Cu NCs catalytic reaction allows the detection of H2O2 in the range of 10 μM to 1 mM with a detection limit of 10 μM. A colorimetric method for glucose detection was also developed by combining the Cu NCs catalytic reaction and the enzymatic oxidation of glucose with glucose oxidase. Taking into account the advantages of ultra-small size, good stability, and high biocompatibility in aqueous solutions, Cu NCs are expected to have potential applications in biotechnology and clinical diagnosis as enzymatic mimics.Graphical abstractHighlights► Copper nanoclusters exhibit peroxidase-like activity for the first time. ► They can catalyze the oxidation of TMB by H2O2 to produce a blue color reaction. ► They have high stability and activity under harsh conditions. ► Copper nanocluster-based colorimetric assays for H2O2 and glucose were developed.

•DNA-Ag nanocluster-based glutathione reductase sensor is reported for the first time.•It is based on fluorescence enhancement in the presence of glutathione reductase.•The present sensor exhibits good selectivity toward glutathione reductase.Fluorescent silver nanoclusters stabilized by DNA (DNA-AgNCs) exhibit distinct response rates to thiol and disulfide. Glutathione reductase can catalyze the reduction of the oxidized glutathione (GSSG) quickly to reduced glutathione (GSH) in the presence of β-nicotinamide adenine dinucleotide 2′-phosphate reduced tetrasodium salt hydrate (NADPH). Consequently, DNA-AgNCs can serve as a new fluorescent platform for assaying the glutathione reductase (GR) activity. This newly proposed assay has a high sensitivity and a good selectivity toward GR. The GR activity can be detected in the range of 0.2–2.0 mU mL−1 with a minimum detectable concentration of 0.2 mU mL−1. Pepsin, lysozyme, trypsin, avidin, thrombin, myoglobin, and BSA have little effect on the fluorescence intensity of DNA-AgNCs. The GR activity assay is successfully used to monitor the inhibition of GR activity by a typical inhibitor 1,3-bis(2-chloroethyl)-1-nitrosourea.Fluorescent silver nanoclusters stabilized by DNA have been used to develop a fluorescent platform for assaying glutathione reductase activity for the first time.

•Visual and SPR absorption Zr4+ sensors have been developed for the first time.•The high affinity between Zr4+ and ATP makes sensor highly sensitive and selective.•A fast response to Zr4+ within 4 min.Owing to its high affinity with phosphate, Zr(IV) can induce the aggregation of adenosine 5′-triphosphate (ATP)-stabilized AuNPs, leading to the change of surface plasmon resonance (SPR) absorption spectra and color of ATP-stabilized AuNP solutions. Based on these phenomena, visual and SPR sensors for Zr(IV) have been developed for the first time. The A660 nm/A518 nm values of ATP-stabilized AuNPs in SPR absorption spectra increase linearly with the concentrations of Zr(IV) from 0.5 μM to 100 μM (r = 0.9971) with a detection limit of 95 nM. A visual Zr(IV) detection is achieved with a detection limit of 30 μM. The sensor shows excellent selectivity against other metal ions, such as Cu2+, Fe3+, Cd2+, and Pb2+. The recoveries for the detection of 5 μM, 10 μM, 25 μM and 75 μM Zr(IV) in lake water samples are 96.0%, 97.0%, 95.6% and 102.4%, respectively. The recoveries of the proposed SPR method are comparable with those of ICP-OES method.Visual and surface plasmon resonance (SPR) sensor for Zr(IV) has been developed for the first time based on Zr(IV)-induced change of SPR absorption spectra of ATP-stabilized AuNP solutions.

Tris(2,2′-bipyridyl)ruthenium(II) electrochemiluminescence (ECL) of glyoxal, glyoxylic acid, methylglyoxal and acetaldehyde has been investigated for the first time, and was compared with ECL of the well-known coreactant oxalate. Glyoxal, glyoxylic acid and methylglyoxal are 4.4-times, 2.5-times and 2.3-times the ECL intensity of oxalate at glassy carbon electrode, respectively. Based on their high ECL efficiencies, glyoxal, methylglyoxal, glyoxylic acid and acetaldehyde have been sensitively detected by ECL methods without the need of derivatization. The ECL intensities increase linearly with the concentrations of glyoxal, glyoxylic acid, methylglyoxal and acetaldehyde over the ranges of 1 μM–10 mM, 1 μM–5 mM, 1 μM–5 mM and 0.3 mM–5 mM, respectively. Electrochemistry studies show that electrogenerated hydroxyl radicals play important roles in ECL, and coreactant family can be expanded by taking advantage of the strong oxidation ability of electrogenerated hydroxyl radicals.Graphical abstractTris(2,2′-bipyridyl)ruthenium(II) electrochemiluminescence of glyoxal, glyoxylic acid, methylglyoxal and acetaldehyde has been investigated for the first time, and is compared with ECL of the well-known coreactant oxalate.Highlights► ECL of glyoxal, glyoxylic acid, and methylglyoxal is studied for the first time. ► They exhibit much stronger ECL than well-known coreactant oxalate at GC electrode. ► They are detected with high sensitivity without derivatization.

2-(Dibutylamino)ethanol (DBAE) is a highly effective coreactant for Ru(bpy)32+ electrochemiluminescence (ECL) and Ru(phen)32+ is a well-known ECL luminophore. In this study, ECL of Ru(phen)32+/DBAE has been investigated for the first time. This study has been carried out using cyclic voltametry and amperometry. The results imply that amperometry is found to be superior to cyclic voltametry as it shows approximately five fold enhancement in ECL emission intensity. Furthermore, compared to Ru(bpy)32+, Ru(phen)32+ provides several fold increase in ECL intensities with DBAE. Sensitive detection of Ru(phen)32+ is achieved with a linear range over approximately four orders of magnitude using very low concentration of DBAE (5 mM).Graphical abstractHighlights► ECL of Ru(phen)32+/DBAE has been investigated for the first time. ► ECL intensities of Ru(phen)32+/DBAE are several times of that of Ru(bpy)32+/DBAE. ► Sensitive detection of Ru(phen)32+ is achieved using very low concentration of DBAE.

A template-free and surfactant-free method for the synthesis of highly monodisperse phenol formaldehyde resin and corresponding carbon nano/microspheres with excellent size tunability has been developed for the first time after investigating a series of phenol derivatives, including 3-methylphenol, 1,3,5-trihydroxybenzene, 2-aminophenol, 3-aminophenol, and 4-aminophenol. The method is based on the polymerization reaction of 3-aminophenol and formaldehyde in the mixture solutions of water and ethanol to generate 3-aminophenol/formaldehyde (APF) resin colloidal spheres. The sizes of APF resin colloidal spheres are tunable in a very broad range from 80 nm up to 2500 nm by changing reaction conditions. The excellent thermal stability of APF resins allows the generation of monodisperse carbon spheres by the pyrolysis of APF resin spheres with high yields. Both APF resin spheres and corresponding carbon spheres are so monodisperse (polydispersity <3%) that can form three-dimensional periodic structures. The method has striking features of excellent monodispersity, very broad size tunability, high yield, smooth sphere surface, and easy preparation. This approach also holds great promise for the large-scale production of resin spheres and carbon spheres.

•A monolithic MIP sensor based on CCE has been reported.•The CCE-based MIP sensor can be renewed simply by polishing.•The as-prepared cholesterol sensor shows good sensitivity.•CCE provides a new versatile platform for constructing monolithic MIP sensors.A monolithic molecular imprinting sensor based on ceramic carbon electrode (CCE) has been reported. The sensor can be renewed simply by smoothing. It was fabricated by thoroughly mixing multiwalled carbon nanotube@molecularly imprinted polymer (MWCNT@MIP), graphite powder, and silicon alkoxide, and then packing the resulting complex mixture of components firmly into the electrode cavity of a Teflon sleeve. The incorporated MWCNT@MIP in CCEs functioned as a recognition element for cholesterol determination. The MWCNT@MIP-CCEs were tested in the presence or absence of cholesterol by cyclic voltammetry and linear sweep voltammetry. The cholesterol sensor has excellent sensitivity with a linear range of 10–300 nM and a detection limit of 1 nM (S/N=3). The monolithic molecular imprinting sensor exhibits good stability, high sensitivity, and user-friendly reusability for cholesterol determination. This study shows that CCE is a promising matrix for MIP sensors.

Many cathodic electrochemiluminescence (ECL) systems require very negative potentials; it is difficult to achieve stable cathodic ECL in aqueous solutions because of hydrogen evolution and instability of intermediates. In this study, tricresyl phosphate-based carbon paste electrode (CPE) was used to achieve cathodic ECL. It exhibits no obvious hydrogen evolution even at a potential up to −1.6 V and dramatically stabilizes electrogenerated [Ru(bpy)3]+. Therefore, a reversible wave of [Ru(bpy)3]2+/1+ in aqueous solutions at carbon electrode has been observed for the first time, and cathodic ECL of [Ru(bpy)3]2+/S2O82− has been achieved. Under the optimum conditions, the plots of the ECL versus the concentration of S2O82− are linear in the range of 10−6 to 10−2 M with the detection limit of 3.98 × 10−7 M. Common anions have no effect on the ECL intensity of the [Ru(bpy)3]2+/S2O82− system. Since CPEs have been widely used, CPEs with high hydrogen evolution potential are versatile platforms for electrochemical study and cathodic ECL study.

Hydrogen evolution bothers stripping analysis significantly. Dioctyl phthalate-based carbon paste electrode exhibits extremely wide cathodic potential window. It is explored as a powerful substrate electrode to solve the problem of hydrogen evolution and further improve reproducibility for stripping analysis using bismuth-coated electrodes for the first time. It was successfully applied to the simultaneous determination of Zn2+, Cd2+, and Pb2+. Linear responses are obtained for Zn2+ in the range of 10–100 μg L−1 and for Pb2+ and Cd2+ in the range of 5–100 μg L−1. The detection limits for Zn2+, Cd2+, and Pb2+ are 0.1 μg L−1, 0.22 μg L−1 and 0.44 μg L−1, respectively. The method has been successfully applied to the determination of Zn2+, Cd2+, and Pb2+ in waste water samples. The detection strategy based on the combination of dioctyl phthalate-based carbon paste electrode and bismuth-coated electrodes holds great promise for stripping analysis.Graphical abstract.Highlights► Dioctyl phthalate-based CPE has extremely wide cathodic potential range. ► It has been used for bismuth-based stripping analysis for the first time. ► It can effectively avoid hydrogen evolution and improve reproducibility. ► It is suitable for detecting more active metals such as zinc. ► It is a powerful platform for bismuth-based electrochemical stripping analysis.

Tris(2,2′-bipyridyl)ruthenium (II) (Ru(bpy)32+) electrochemiluminescence is one of the most successful electrochemiluminescent systems and has broad range of applications. Most analytical applications of tris(2,2′-bipyridyl)ruthenium (II) electrochemiluminescence involve coreactants. We comprehensively review typical coreactants, such as oxalate, persulfate, tripropylamine (TPA), NADH (Nicotinamide adenine dinucleotide, reduced disodium salt), 2-(dibutylamino)ethanol, vitamin C derivatives, alcohols, ketones, nucleic acid, formic acid, formaldehyde, organic acids, amines, hydrogen peroxide, oxygen, hydrazine and relative derivatives. The electrochemiluminescent mechanisms are described correspondingly. Furthermore, some perspectives on coreactants are also discussed.

Fluorescence nanoclusters have been used for the determination of melamine for the first time. The method is based on the fluorescence turn-on of oligonucleotide-stabilized silver nanoclusters (DNA–Ag NCs) by melamine. The enhancement factors (I−I0)/I0 increase linearly with melamine concentrations over the range 5.0×10−8–7.0×10−6 M (R2=0.998). The detection limit is 1.0×10−8 M, which is approximately 2000 times lower than the US Food and Drug Administration estimated melamine safety limit of 20.0 μM. Furthermore, the milk samples spiked with melamine are analyzed with excellent recoveries.Highlights► Fluorescent nanoclusters have been used for detecting melamine for the first time. ► It bases on fluorescence turn-on of nanoclusters by melamine. ► The fluorescent nanocluster used is oligonucleotide-stabilized silver. ► The method shows nice sensitivity. ► The milk samples spiked with melamine are analyzed with good recoveries.

Noble metal nanocrystals with high-energy facets have attracted extensive attention due to their unique properties and potential applications. This review encompasses the most recent progress of both synthesis and applications of noble metal nanocrystals with high-energy facets. First, typical shapes of noble metal nanocrystals with high-energy facets are introduced. Then, the synthesis methods of noble metal nanocrystals enclosed by {1 1 0} and {h k l} high-index facets are presented, with an emphasis of their formation mechanisms. Third, surface-enhanced properties and applications of noble metal nanocrystals with high-energy facets are highlighted. Finally, challenges and opportunities of shape control of noble metal nanocrystals with high-energy facets are presented.Graphical abstractHighlights► Recent advances in noble metal nanocrystals with {1 1 0} and {h k l} high-energy facets. ► Shapes and crystal facets of noble metal nanocrystals with high-energy facets. ► Synthesis strategies for noble metal nanocrystals with high-energy facets. ► A summary of existing parameters to control the growth of high-energy facets. ► Superior properties of noble metal nanocrystals with high-energy facets.

In this study, fluorescent metal nanoclusters are presented as novel probes for sensitive detection of protease for the first time. The sensing mechanism is based on trypsin digestion of the protein template of BSA-stabilized Au nanoclusters. The decrease in fluorescence intensity of BSA-Au nanoclusters caused by trypsin allows the sensitive detection of trypsin in the range of 0.01–100 μg/mL. The detection limit for trypsin is 2 ng/mL (86 pM) at a signal-to-noise ratio of 3. The present nanosensor for trypsin detection possesses red emission, excellent biocompatibility, high selectivity, and good stability. In addition, we demonstrated the application of the present approach in real urine samples, which suggested its potential for diagnostic purposes.Highlights► Fluorescent nanocluster is a novel protease sensing platform. ► The detection bases on trypsin digestion of BSA-stabilized Au nanoclusters. ► The fluorescence of BSA-stabilized Au nanoclusters depends on trypsin concentrations. ► The proposed method is the most sensitive fluorescent method for trypsin detection.

This review highlights work from the authors’ laboratory on the recent development of seed-mediated growth method for noble metal nanocrystals. The seed-mediated growth method has become one of the most efficient and versatile methods for synthesizing high-quality noble metal nanocrystals. The seed-mediated growth method can separate the nucleation and growth stages of metal nanocrystals, and thus provide better control over the size, size distribution, and crystallographic evolution of metal nanocrystals. Because of its high controllability, the seed-mediated growth method is especially promising in providing mechanistic insights into the growth mechanisms of noble metal nanocrystals. In this review, the thermodynamic and kinetic parameters for the nucleation and growth of noble metal nanocrystals are systematically summarized. Mechanistic understanding of these parameters is provided. These studies provide useful guidelines for the rational design and synthesis of novel noble metal nanocrystals with high quality.

Single-walled carbon nanohorns have been used to construct an aptasensor for the first time. This novel aptasensor was successfully used for the detection of thrombin with high sensitivity and excellent selectivity. This thrombin aptasensor has a detection limit of as low as 100 pM.

In synthesis in a solution phase, adsorbates such as halides can interact selectively with different metal crystal facets and affect the final morphology of nanocrystals. Pseudo-halide thiocyanate ions (SCN−) can also adsorb on the metal surface, but they have never been used for the synthesis of shape-controlled colloidal metal nanocrystals. In this study, we first investigated the effect of SCN− on the morphology of palladium nanocrystals through a seed-mediated growth method. The presence of 1 µM SCN− in the growth solutions could lead to the formation of palladium polyhedra: truncated rhombic dodecahedra enclosed by twelve {110}, eight {111} and six {100} facets. The products were nanocubes enclosed with six {100} facets if cetyltrimethylammonium bromide (CTAB) was the only capping agent. Meanwhile, the mechanism of the effect of SCN− on the morphology of Pd nanocrystals is discussed.

A label-free supersandwich electrochemiluminescence assay based on T–Hg2+–T coordination and the intercalation of Ru(phen)32+ for Hg2+ analysis was developed with excellent sensitivity and selectivity.

Concave trisoctahedral (TOH) Pd@Au core–shell nanocrystals bound by {331} facets have been synthesized for the first time. Pd nanocubes and cetyltrimethylammonium chloride were used as the structure-directing cores and capping agents, respectively. Their optical and electrocatalytic properties were investigated.

In this communication, we demonstrate for the first time the proof of concept that single-walled carbon nanohorns can be used as an effective fluorescent sensing platform for nucleic acid detection with a high selectivity down to single-base mismatch.

We reported a versatile strategy for electrochemical determination of H2O2 as well as related enzymes and substrates by combining the advantages of H2O2-mediated selective boronate deprotection and p-aminophenol for the first time. H2O2 is selectively detected through the determination of p-aminophenol generated from H2O2-mediated boronate deprotection of p-aminophenylboronic acid. This method allows H2O2 detection in the range from 1 μM to 1 mM with a detection limit of 0.8 μM. Since many enzymes and their substrates can be detected through the determination of H2O2, we extend this method to detect related enzymes and their substrates using glucose and glucose oxidase as representative analytes. There is a good linear relationship between the current responses and GOx activity from 0.01 U/mL to 0.8 U/mL with a detection limit of 0.01 U/mL. The method is promising for broad and important applications, such as driver alcohol detection as well as clinical analysis of glucose, uric acid, lactate, glutamate, and so on.Highlights► A versatile method to detect H2O2 and related enzymes and substrates is developed. ► The detection of H2O2 is based on selective H2O2-mediated boronate deprotection. ► Related enzymes and substrates are detected through the determination of H2O2.

Vitamin C derivatives (VCDs) have been widely used as the alternative and stable sources of vitamin C, and accordingly exhibit many new applications, such as anti-tumor and central nervous system drug delivery. In this study, their Ru(bpy)32+ electrochemiluminescence (ECL) properties have been investigated for the first time using well-known ascorbyl phosphate and ascorbyl palmitate as representative VCDs. Ascorbyl phosphate and ascorbyl palmitate are VCDs with different substituted positions. Both of them increase Ru(bpy)32+ ECL, indicating that other VCDs may also enhance Ru(bpy)32+ ECL signal. The calibration plot for ascorbyl phosphate is linear from 3 × 10−6 to 1.0 × 10−3 M with a detection limit of 1.4 × 10−6 M at a signal-to-noise ratio of 3. The relative standard deviation is 3.6% for six replicate measurements of 0.01 mM ascorbyl 2-phosphate solution. The proposed method is about one order of magnitude more sensitive than electrochemical and UV–vis methods for the determination of ascorbyl phosphate, and is used successfully for the determination of ascorbyl phosphate in whitening and moisturising body wash.Graphical abstractHighlights► Ru(bpy)32+ electrochemiluminescence of vitamin C derivatives have been investigated. ► Ascorbyl phosphate and ascorbyl palmitate show intense electrochemiluminescence. ► Ascorbyl 2-phosphate was detected with high sensitivity. ► This study provides a new way to detect vitamin C derivatives.

Two new electrochemiluminescence (ECL) systems, the Ru(bpy)32+/formaldehyde system and the Ru(bpy)32+/formic acid system, have been reported. Intense ECL was observed from Ru(bpy)32+ in the presence of formaldehyde or formic acid at glassy carbon electrodes, but not at platinum and gold electrodes. The ECL reactions may involve the oxidation of formaldehyde and formic acid by electrogenerated OH to form the strong reducing intermediates CHO and CO2− that react with Ru(bpy)33+ to emit light. The ECL intensity increases linearly with the formaldehyde or formic acid concentration over the range of concentration of 3 μM–1 mM. The detection limit is 1 μM for formaldehyde and formic acid.

In this study, we report the electrochemiluminescence (ECL) of tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)32+) in the presence of hydrazine and its derivatives in solution phase for the first time. Hydrazine and isoniazid were found to be able to enhance the ECL of Ru(bpy)32+, while phenylhydrazine and hydroxylamine were observed to decrease the ECL. The possible ECL mechanisms are discussed, and the method was used to detect hydrazine and isoniazid in aqueous solutions. Under the optimum experimental conditions, the dynamic ranges were 10−7–10−3 M and 10−6–10−3 M for hydrazine and isoniazid, respectively. The detection limits were 3.8 × 10−8 M for hydrazine and 4.8 × 10−7 M for isoniazid. The proposed method has been applied to detect the content of isoniazid in pharmaceutical samples with satisfactory results.

Aptamers have been widely used for the detection of target molecules owing to their chemical stability, easy modification and remarkable specificity and affinity for various target molecules. Electrochemical methods are well known for low cost, high sensitivity and usage of miniature instruments. Recently, the design of electrochemical aptasensors has attracted significant attention in the field of biosensors. This paper mainly reviews the developments of these aptasensors since 2005, and discusses the prospects.

This review provides an overview of recent developments in the controlled synthesis of well-defined noble metal nanocrystals from the viewpoint of crystallographic control. Discussions are focused on the relationship between the shapes of noble metal nanocrystals and their internal and external crystal structures. Representative strategies for the crystallographic control of noble metal nanocrystals are introduced and discussed from the aspects of internal and external crystallographic control. Typical examples of the enhanced properties of noble metal nanocrystals by crystallographic control are highlighted.Graphical abstractHighlights► The shapes of metal nanocrystals depend on their internal and external structures. ► An overview of representative strategies for crystallographic control is given. ► Enhanced properties of metal nanocrystals by crystallographic control are introduced.

Combining the advantages of signal-on strategy and nicking endonuclease assisted electrochemistry signal amplification (NEAESA), a new sensitive and signal-on electrochemical DNA biosensor for the sequence specific DNA detection based on NEAESA has been developed for the first time. A Hairpin-shape probe (HP), containing the target DNA recognition sequence, is thiol-modified at 5′ end and immobilized on gold electrode via Au–S bonding. Subsequently, the HP modified electrode is hybridized with target DNA to form a duplex. Then the nicking endonuclease is added and nicks the HP strand in the duplex. After nicking, 3′-ferrocene (Fc)-labeled part complementary probe (Fc-PCP) is introduced on the electrode surface by hybridizing with the thiol-modified HP fragment, which results in the generation of electrochemical signal. Hence, the DNA biosensor is constructed successfully. The present DNA biosensor shows a wide linear range of 5.0 × 10−13–5.0 × 10−8 M for detecting target DNA, with a low detection limit of 0.167 pM. The proposed strategy does not require any amplifying labels (enzymes, DNAzymes, nanoparticles, etc.) for biorecognition events, which avoids false-positive results to occur frequently. Moreover, the strategy has the benefits of simple preparation, convenient operation, good selectivity, and high sensitivity. With the advantages mentioned above, this simple and sensitive strategy has the potential to be integrated in portable, low cost and simplified devices for diagnostic applications.

Because of its unique pore network, good strength, and low cost, cement was used as a new electrode material and solid-phase microextraction (SPME) material for the first time. It was mixed with carbon to make a new electrode, cement carbon electrode (CCE). The as-prepared CCE was used to demonstrate the application of cement in SPME by Ru(bpy)32+ electrochemiluminescent detection of perphenazine (PPZ). The calibration plot for PPZ is linear from 1.0 × 10−9 to 3.0 × 10−6 M with a detection limit of 3.1 × 10−10 M. The method was successfully applied to the detection of PPZ in urine sample. Cement-based electrode material may also find broad applications in electrochemistry industry, such as electrochemical wastewater treatment.

Electrochemiluminescence (ECL) is chemiluminescence triggered by electrochemical techniques. More than 150 ECL assays with remarkably high sensitivity and extremely wide dynamic range are currently available, and accounts for hundreds of millions of dollars in sales per year. The recent development of ECL is particularly rapid. After a brief introduction to ECL, this critical review presents the active and/or emerging areas of ECL research as well as new applications and phenomena of ECL, such as light-emitting electrochemical cell, wireless electrochemical microarray using ECL as photonic reporter, high throughput analysis, aptasensors, immunoassays and DNA analysis, ECL of nanoclusters and carbon nanomaterials, ECL imaging techniques, scanning ECL microscopy, colorimetric ECL sensor, surface plasmon-coupled ECL, electrostatic chemiluminescence, soliton-like ECL waves, ECL investigation of molecular interaction, and single molecule detection. Finally, some perspectives on this rapidly developing field are discussed (322 references).

Single-walled carbon nanohorns (SWCNHs) are horn-shaped single-walled tubules with a conical tip. They are generally synthesized by laser ablation of pure graphite without using metal catalyst with high production rate and high yield, and typically form radial aggregates. SWCNHs are essentially metal-free and very pure, which avoids cumbersome purification and makes them user-friendly and environmentally benign. Currently, SWCNHs have been widely studied for various applications, such as gas storage, adsorption, catalyst support, drug delivery system, magnetic resonance analysis, electrochemistry, biosensing application, photovoltaics and photoelectrochemical cells, photodynamic therapy, fuel cells, and so on. This review outlines the research progress on SWCNHs, including their properties, functionalization, applications, and outlook.

The carbon electrode was covalently modified by electrochemical reduction of nitro precursor in the presence of NaNO2 in aqueous solutions. The nitro precursor used is p-nitrophenyl phosphate, a well-known chromogenic substrate for the determination of acid and alkaline phosphatases. It is the first method for the covalent modification of carbon surface with a phosphate group. The modified electrode was characterized via cyclic voltammetry, electrochemical impedance spectroscopy, and X-ray photoelectron spectroscopy. It displays good electrocatalytic activity toward hydrogen peroxide reduction.

A tantalum electrode is reported as an alternative electrode for electrochemical stripping analysis for the first time. Several key operational parameters that influenced the electroanalytical signals were optimized, such as pH of the electrolyte, deposition potential and deposition time. The tantalum electrode yields well-defined and sharp stripping signals for trace cadmium analysis when combined with differential pulse anodic stripping voltammetry. Under the optimized condition the electrode shows good linear behavior in the examined concentration in the range of 20–200 μg L−1 for cadmium, with a detection limit (3σ) of 0.57 μg L−1 followed a 5-min deposition step under − 1.3 V. It also shows good reproducibility with a relative standard deviation of 2.56% for ten consecutive measurements. The sensor was also employed for real sample determination and exhibited excellent performance compared with the result of inductively coupled plasma-mass spectrometry.

It has been reported that electrogenerated chemiluminescence (ECL) of the tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)32+)/pyruvate system cannot be observed unless cerium(III) is employed to oxidize pyruvate since it is difficult to oxidize pyruvate either directly on the electrode or by electrogenerated Ru(bpy)33+. In this study, we find that ECL of the Ru(bpy)32+/pyruvate system can be observed in the absence of cerium(III) at gold, platinum, glassy carbon, and carbon paste electrodes by using slow scan rate. The slow scan rate may favor the oxidation of more pyruvate and reduce background signal, and thus leads to generation of ECL of the Ru(bpy)32+/pyruvate system. This finding provides an alternative approach for the determination of pyruvate. Under the optimum conditions, the plots of the ECL versus the concentration of pyruvate is linear in the range of 5.0 × 10−6 M∼1.0 × 10−4 M with the detection limit of 5.0 × 10−6 M. The relative standard deviation is 5.08% for nine consecutive measurements of 5.0 × 10−5 M pyruvate.

ECL of several amines containing different numbers of hydroxyl and amino groups was investigated. N-butyldiethanolamine is found to be more effective than 2-(dibutylamino)ethanol at gold and platinum electrodes, and is the most effective coreactant reported until now. Surprisingly, ECL intensities of monoamines, such as 2-(dibutylamino)ethanol and N-butyldiethanolamine, are much stronger than that of diamines including N,N,N′,N′-tetrakis-(2-hydroxyethyl)-ethylenediamine and N,N,N′,N′-tetrakis-(2-hydroxypropyl)ethlenediamine. The striking contrast between ECL signals of the investigated monoamines and diamines may result from more significant side reactions of diamines, such as the intramolecular side reactions between oxidative amine cation radicals and reductive amine free radicals.

Single-walled carbon nanohorns (SWNHs), distinguished by their high purity and distinct structure, were noncovalently functionalized with poly(sodium 4-styrenesulfonate). The functionalized SWNHs were characterized by scanning electron microscopy, atomic force microscopy, ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and thermogravimetry. Heme protein myoglobin was adsorbed onto surface of functionalized SWNHs to prepare electrochemical biosensor. Surface assembly process and direct electrochemistry of immobilized myoglobin were investigated by electrochemical impedance spectroscopy and cyclic voltammetry, respectively. The proposed biosensor exhibited good electrocatalysis to the reduction of hydrogen peroxide. The response was linear over the range 3–350 μM with a detection limit of 0.5 μM. Good reproducibility and stability of the biosensor were obtained toward hydrogen peroxide detection.

A versatile method for selectively synthesizing single-crystalline rhombic dodecahedral, cubic, and octahedral palladium nanocrystals, as well as their derivatives with varying degrees of edge- and corner-truncation, was reported for the first time. This is also the first report regarding the synthesis of rhombic dodecahedral palladium nanocrystals. All the nanocrystals were readily synthesized by a seed-mediated method with cetyltrimethylammonium bromide as surfactant, KI as additive, and ascorbic acid as reductant. At the same ascorbic acid concentration, a series of palladium nanocrystals with varying shapes were obtained through manipulation of the concentration of KI and the reaction temperature. The formation of different palladium facets were correlated with their growth conditions. In the absence of KI, the {100} palladium facets are favored. In the presence of KI, the concentration of KI and the reaction temperature play an important role on the formation of different palladium facets. The {110} palladium facets are favored at relatively high temperatures and medium KI concentrations. The {111} palladium facets are favored at relatively low temperatures and medium KI concentrations. The {100} palladium facets are favored at either very low or relatively high KI concentrations. These correlations were explained in terms of surface-energy and growth kinetics. These results provide a basis for gaining mechanistic insights into the growth of well-faceted metal nanostructures.Keywords: crystal growth; nanostructures; palladium; rhombic dodecahedron; shape control

[Ru(bpy)2dppz]2+ electrochemiluminescence (ECL) was studied, and it was used to investigate DNA interaction and develop a label-free ATP aptasensor for the first time. ECL of [Ru(bpy)2dppz]2+ is negligible in aqueous solution, and increases ∼1000 times when [Ru(bpy)2dppz]2+ intercalates into the nucleic acid structure. The ECL switch behavior of [Ru(bpy)2dppz]2+ is ascribed to the intercalation that shields the phenazine nitrogens from the solvent and results in a luminescent excited state. The ECL switch by DNA was applied to investigate the interaction of [Ru(bpy)2dppz]2+ with herring sperm DNA. The calculated equilibrium constant (K) is 1.35 × 106 M−1, and the calculated binding-site size (s) is 0.88 base pair, which is consistent with the reported values. Moreover, ATP can dramatically affect ECL of the [Ru(bpy)2dppz]2+/ATP aptamer complex. As a result, a label-free, sensitive, and selective [Ru(bpy)2dppz]2+ ECL method for ATP detection was developed. The detection limit is 100 nM for ATP (with a signal-to-noise ratio, S/N, of 3) with a linear range of 0−1 μM. The result demonstrates that [Ru(bpy)2dppz]2+ ECL holds great promise in aptasensors.

Carbon modified by the reduction of aromatic diazonium derivatives was first used as electrode for the electrochemical stripping analysis of heavy metals. As a model, the glassy carbon electrode was modified with benzoic acid by electrochemical reduction of diazobenzoic acid, and the resulting modified electrodes were used for determination of Cd2+ and Pb2+. The anodic peak currents of cadmium and lead at the benzoic acid-modified glassy carbon electrode are 7.2 and 6 times of that at the bare glassy carbon electrode. A linear response was observed for Pb2+ and Cd2+ in the range of 0.5–50 μg/l. The detection limits are 0.20 μg/l for Pb2+ and 0.13 μg/l for Cd2+. The relative standard deviations for six consecutive measurements of 50 μg/l Cd2+ and 50 μg/l Pb2+ are 0.82% and 3.02%, respectively. Applicability of the sensor to the determination of Cd2+ and Pb2+ in sewerage samples was demonstrated.

Single-walled carbon nanohorn modified glassy carbon electrode (SWCNH-modified GCE) was first employed for the simultaneous determination of uric acid (UA), dopamine (DA), and ascorbic acid (AA). The SWCNH-modified GCE displayed excellent electrochemical catalytic activities. The oxidation overpotentials of UA, DA, and AA decrease significantly and their oxidation peak currents increase dramatically at SWCNH-modified GCE. Linear sweep voltammetry (LSV) was used for the simultaneous determination of UA, DA, and AA in their ternary mixture. The peak separations between UA and DA, and DA and AA are large up to 152 mV and 221 mV, respectively. The calibration curves for UA, DA, and AA were obtained in the range of 0.06–10 μM, 0.2–3.8 μM, and 30–400 μM, respectively. The detection limits (S/N = 3) were 20 nM, 60 nM, and 5 μM for UA, DA, and AA, respectively. The proposed method improved sensitivity for the determination of UA by more than one order of magnitude. The present method was applied to the determination of UA, DA, and AA in urine sample by using standard adding method and the results were satisfactory.

Single-walled carbon nanohorns (SWCNHs) were used as a novel and biocompatible matrix for fabricating biosensing devices. The direct immobilization of acid-stable and thermostable soybean peroxidase (SBP) on SWCNH modified electrode surface can realize the direct electrochemistry of enzyme. Cyclic voltammogram of the adsorbed SBP displays a pair of redox peaks with a formal potential of −0.24 V in pH 5 phosphate buffer solution. The formal potential has a linear relationship with pH from 3 to 9 with a slope of −48.7 mV/pH, close to the value of −55.7 mV/pH expected at 18 °C for the reversible transfer of one proton and one electron. Bioactivity of SBP remains good in SWCNH microenvironment, along with effective catalysis of the reduction of H2O2. In the absence of a mediator, this H2O2 biosensor exhibited a high sensitivity (16.625 μA L/mmol), a linear range from 0.02 to 1.2 mmol L−1, and a detection limit of 5.0 × 10−7 mmol L−1, as well as acceptable preparation reproducibility and excellent stability.

Single-walled carbon nanohorn (SWCNH) was developed as new adsorbent for solid-phase extraction using 4-nitrophenol as representative. The unique exoteric structures and high surface area of SWCNH allow extracting a large amount of 4-nitrophenol over a short time. Highly sensitive determination of 4-nitrophenol was achieved by linear sweep voltammetry after only 120 s extraction. The calibration plot for 4-nitrophenol determination is linear in the range of 5.0 × 10−8 M–1.0 × 10−5 M under optimum conditions. The detection limit is 1.1 × 10−8 M. The proposed method was successfully employed to determine 4-nitrophenol in lake water samples, and the recoveries of the spiked 4-nitrophenol were excellent (92–106%).

An electrochemiluminescence (ECL) sensor based on Ru(bpy)32+–graphene–Nafion composite film was developed. The graphene sheet was produced by chemical conversion of graphite, and was characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), and Raman spectroscopy. The introduction of conductive graphene into Nafion not only greatly facilitates the electron transfer of Ru(bpy)32+, but also dramatically improves the long-term stability of the sensor by inhibiting the migration of Ru(bpy)32+ into the electrochemically inactive hydrophobic region of Nafion. The ECL sensor gives a good linear range over 1 × 10−7 to 1 × 10−4 M with a detection limit of 50 nM towards the determination of tripropylamine (TPA), comparable to that obtained by Nafion-CNT. The ECL sensor keeps over 80% and 85% activity towards 0.1 mM TPA after being stored in air and in 0.1 M pH 7.5 phosphate buffer solution (PBS) for a month, respectively. The long-term stability of the modified electrode is better than electrodes modified with Nafion, Nafion–silica, Nafion–titania, or sol–gel films containing Ru(bpy)32+. Furthermore, the ECL sensor was successfully applied to the selective and sensitive determination of oxalate in urine samples.

A carbon-supported palladium catalyst modified by non-metal phosphorus (PdP/C) has been developed as an oxygen reduction catalyst for direct methanol fuel cells. The PdP/C catalyst was prepared by the sodium hypophosphite reduction method. The as-prepared Pd nanoparticles have a narrow size distribution with an average diameter of 2 nm. Energy dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) results indicate that P enters into the crystal lattice of Pd and forms an alloy. The PdP/C catalyst has an oxygen reduction reaction (ORR) activity comparable to the commercial Pt/C catalyst and a higher activity than the Pd/C catalyst synthesized by the conventional NaBH4 reduction method. Its high catalytic activity can be attributed to its small size, lower relative crystallinity, and the formation of PdP alloy.

An electrochemiluminescent glucose biosensor was proposed based on gold nanoparticle-catalyzed luminol electrochemiluminescence (ECL). Gold nanoparticles were self-assembled onto silica sol–gel network, and then glucose oxidase was adsorbed on the surface of gold nanoparticles. The surface assembly process and the electrochemistry and ECL behaviors of the biosensor were investigated. The assembled gold nanoparticles could efficiently electrocatalyze luminol ECL. ECL intensity of the biosensor depended on scan rate, luminol concentration, and size of gold nanoparticles. The response of the ECL biosensor was linear over the range 1 μM to 5 mM with a detection limit of 0.2 μM glucose and showed satisfying reproducibility, stability and selectivity.

Single-walled carbon nanohorn (SWCNH) paste electrode was used for amperometric determination of concentrated hydrogen peroxide, and was compared with other carbon electrodes. The calibration plots are linear from 0.5 to 100 mM at activated SWCNH paste electrode and edge plane graphite (EPG) electrode. In contrast, the calibration plots are linear only at concentrations lower than 45 mM at graphite paste electrode, multi-walled carbon nanotube paste electrode, and glassy carbon electrode. Our results show that SWCNH paste electrode and EPG electrode are interesting alternatives to high surface area platinum electrode for determination of concentrated hydrogen peroxide. Because of its high-purity, metal-free SWCNH is a user-friendly and attractive material for electrochemical study.

Nearly monodisperse Pd nanocubes with controllable sizes were synthesized through a seed-mediated growth approach. By using Pd nanocubes of 22 nm in size as seeds, the morphology of the as-grown nanostructures was fixed as single-crystalline, which enabled us to rationally tune the size of Pd nanocubes. The formation mechanism of initial 22 nm nanocubes was also discussed. The size-dependent surface plasmon resonance properties of the as-synthesized Pd nanocubes were investigated. Compared with previous methods, the yield, monodispersity, perfection of the shape formation, and the range of size control of these nanocubes are all improved. These Pd nanocubes may have potential interests in surface-enhanced Raman scattering, sensors, catalysis, study of size-dependent properties, and fabrication of high-order structures.

The biosensing application of single-walled carbon nanohorns (SWCNHs) was demonstrated through fabrication of an amperometric glucose biosensor. The biosensor was constructed by encapsulating glucose oxidase in the Nafion–SWCNHs composite film. The cyclic voltammograms for glucose oxidase immobilized on the composite film displayed a pair of well-defined and nearly symmetric redox peaks with a formal potential of −0.453 V. The biosensor had good electrocatalytic activity toward oxidation of glucose. To decrease detection potential, ferrocene monocarboxylic acid was used as a redox mediator. The mediated glucose biosensor shows a linear range from 0 to 6.0 mM. The biosensor shows high sensitivity (1.06 μA/mM) and stability, and can avoid the commonly coexisted interference. Because of impressive properties of SWCNHs, such as high purity and high surface area, SWCNHs and their composites are expected to be promising material for biomolecular immobilization and biosensing applications.

The high hydrogen evolution overpotential of a bismuth electrode makes it a powerful electrode for cathodic electrochemiluminescence studies in aqueous solutions.

Rotating minidisk–disk electrode (RMDDE) was developed by replacing ring electrode of rotating ring–disk electrode (RRDE) with a minidisk electrode. Its applications were demonstrated by studying electrochemical reactions of ferricyanide and divalent copper. The replacement of ring electrode by minidisk electrode results in following advantages. First, the fabrication of RMDDE is easier than that of RRDE with the same electrode material. Second, there is more freedom in choosing electrode materials and sizes, since it is difficult to make thin ring electrodes of RRDE with fragile materials. Third, the replacement of ring electrode by minidisk electrode saves electrode materials, especially rare materials. Finally, the substitution of minidisk electrode for ring electrode allows using multiple minidisks for simultaneous monitoring of multiple components. Therefore, RMDDE is a promising generator–collector system, especially when special generator–collector systems are not commercially available, such as corrosion study and electrocatalysis study of new electrode materials.

Previous studies show that aromatic diols inhibited Ru(bpy)32+ electrochemiluminescence (ECL), and all reported Ru(bpy)32+ ECL methods for the determination of aromatic diols-containing coreactants are based on inhibition of Ru(bpy)32+/tripropylamine ECL. In this study, the interaction between diol and borate anion was exploited for Ru(bpy)32+ ECL detection of coreactants containing aromatic diol group using epinephrine as a model analyte. The interaction prevented from the inhibition of Ru(bpy)32+ ECL by aromatic diol group of epinephrine. As a result, epinephrine was successfully detected in the absence of tripropylamine simply by using borate buffer solution as the supporting electrolyte. Under the optimum conditions, the log of the ECL intensity increases linearly with the log of epinephrine concentrations over the concentration range of 1.0 × 10−9–1.0 × 10−4 M. The detection limit is 5.0 × 10−10 M at a signal-to-noise ratio of three. The proposed method exhibit wider dynamic range and better detection limit than that by inhibited Ru(bpy)32+ ECL method. The relative standard deviation for 14 consecutive determinations of 5 μM epinephrine was 3.5%. The strategy by interaction with borate anion or boronate derivatives is promising for the determination of coreactants containing aromatic diol group or aromatic hydroxyl acid group. Such interaction can also be used to avoid interference from aromatic diols or aromatic hydroxyl acids.

Electrochemiluminescence (ECL) is chemiluminescence triggered by electrochemical techniques. More than 150 ECL assays with remarkably high sensitivity and extremely wide dynamic range are currently available, and accounts for hundreds of millions of dollars in sales per year. The recent development of ECL is particularly rapid. After a brief introduction to ECL, this critical review presents the active and/or emerging areas of ECL research as well as new applications and phenomena of ECL, such as light-emitting electrochemical cell, wireless electrochemical microarray using ECL as photonic reporter, high throughput analysis, aptasensors, immunoassays and DNA analysis, ECL of nanoclusters and carbon nanomaterials, ECL imaging techniques, scanning ECL microscopy, colorimetric ECL sensor, surface plasmon-coupled ECL, electrostatic chemiluminescence, soliton-like ECL waves, ECL investigation of molecular interaction, and single molecule detection. Finally, some perspectives on this rapidly developing field are discussed (322 references).

The high hydrogen evolution overpotential of a bismuth electrode makes it a powerful electrode for cathodic electrochemiluminescence studies in aqueous solutions.

A label-free supersandwich electrochemiluminescence assay based on T–Hg2+–T coordination and the intercalation of Ru(phen)32+ for Hg2+ analysis was developed with excellent sensitivity and selectivity.

Concave trisoctahedral (TOH) Pd@Au core–shell nanocrystals bound by {331} facets have been synthesized for the first time. Pd nanocubes and cetyltrimethylammonium chloride were used as the structure-directing cores and capping agents, respectively. Their optical and electrocatalytic properties were investigated.

In this study, we report the electrochemiluminescence (ECL) of tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)32+) in the presence of hydrazine and its derivatives in solution phase for the first time. Hydrazine and isoniazid were found to be able to enhance the ECL of Ru(bpy)32+, while phenylhydrazine and hydroxylamine were observed to decrease the ECL. The possible ECL mechanisms are discussed, and the method was used to detect hydrazine and isoniazid in aqueous solutions. Under the optimum experimental conditions, the dynamic ranges were 10−7–10−3 M and 10−6–10−3 M for hydrazine and isoniazid, respectively. The detection limits were 3.8 × 10−8 M for hydrazine and 4.8 × 10−7 M for isoniazid. The proposed method has been applied to detect the content of isoniazid in pharmaceutical samples with satisfactory results.

It has been reported that electrogenerated chemiluminescence (ECL) of the tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)32+)/pyruvate system cannot be observed unless cerium(III) is employed to oxidize pyruvate since it is difficult to oxidize pyruvate either directly on the electrode or by electrogenerated Ru(bpy)33+. In this study, we find that ECL of the Ru(bpy)32+/pyruvate system can be observed in the absence of cerium(III) at gold, platinum, glassy carbon, and carbon paste electrodes by using slow scan rate. The slow scan rate may favor the oxidation of more pyruvate and reduce background signal, and thus leads to generation of ECL of the Ru(bpy)32+/pyruvate system. This finding provides an alternative approach for the determination of pyruvate. Under the optimum conditions, the plots of the ECL versus the concentration of pyruvate is linear in the range of 5.0 × 10−6 M∼1.0 × 10−4 M with the detection limit of 5.0 × 10−6 M. The relative standard deviation is 5.08% for nine consecutive measurements of 5.0 × 10−5 M pyruvate.

In this communication, we demonstrate for the first time the proof of concept that single-walled carbon nanohorns can be used as an effective fluorescent sensing platform for nucleic acid detection with a high selectivity down to single-base mismatch.

Tetrahexahedral, polyhedral, and branched Pd@Au core–shell nanostructures were selectively produced by manipulating their growth thermodynamics and kinetics. The current density in the electrochemical oxidation of H2O2 and the electrochemiluminescence density of luminol–H2O2 systems at the tetrahexahedron modified electrode are 43.5 and 16.4 times that at the bulk Au electrode, respectively.