Correction for ‘Controlled size and morphology, and phase transition of YF3:Yb3+,Er3+ and YOF:Yb3+,Er3+ nanocrystals for fine color tuning’ by Yongsheng Zhu et al., J. Mater. Chem. C, 2016, DOI: 10.1039/c5tc03473f.

Lanthanide rare-earth (RE) based upconversion nanocrystals (UCNCs) have the ability to generate visible emission as well as a wide range of applications under near-infrared excitation. However, each lanthanide ion has a unique set of energy levels and generally exhibits a set of sharp emission peaks. Nowadays, it is very important to finely tune the upconversion (UC) properties through controlling the particle size, crystalline phase and shape of UCNCs. Herein, we reported the systematic synthesis and fine control of monodisperse rare-earth doped fluoride and oxyfluoride nanocrystals (NCs) in the same reaction system. When the ratios of oleic acid (OA) to oleylamine (OM) decreased from 4:1 to 3:8, the shapes of NCs changed from rhombic nanoplates to small spherical nanoparticles (~2 nm), while the crystalline phases changed from the orthorhombic phase (YF3) to the tetragonal phase (YOF). Furthermore, it is interesting to observe that the emission color changed from green to red with the transformation of both the crystalline phase and shape, which can broaden the applications of rare-earth based nanomaterials ranging from displays to bioimaging.

A single-nanoparticle plasmonic sensor for the sensitive detection of gas molecules (NO2) has been constructed. Taking advantage of active molecular plasmonics, the analyte selectively triggers a measurable spectral shift of ferrocene-modified single gold nanorods.

We developed a route for synthesizing Ag nanostructures with tunable morphologies for ultrasensitive surface-enhanced Raman spectroscopy. Through the consecutive addition of three reducing agents (i.e., 4-mercaptobenzoic acid, trisodium citrate, and ascorbic acid) to an aqueous solution of silver nitrate, hierarchical flower-like Ag nanostructures were produced. The nanostructures had Ag petals in which nanosized gaps were generated, and small Ag nanoparticles were incorporated within the gaps. Theoretically, the nanostructures exhibited highly enhanced electric fields in the outer-shell regions where the small Ag nanoparticles were densely located. Combining the enhanced field effect with resonance effect of a Raman-active molecule (methylene blue) at a specific wavelength, measurable Raman signals were obtained at concentrations as low as 100 attomolar (10–16 M; corresponding to 10–21 mol). Key factors were discussed for the synthesis of the Ag nanostructures while finely controlling the morphologies of hierarchical Ag nanostructures, thereby modulating the intensity of surface-enhanced resonance Raman spectroscopy (SERRS) signals. Therefore, this synthetic method produces highly promising nanostructures for SERRS-based applications.Keywords: morphology tuning; nanoparticles incorporated branches; SERRS; silver nanostructures; ultrasensitive detection;

A novel permeability gate-based electrochemiluminescent (ECL) aptasensor has been constructed by utilizing target-responsive polyelectrolyte–aptamer film deposited on the solid-state ECL electrode to control the rate of diffusion of a coreactant that triggers the ECL.

Proteases and nucleases are enzymes heavily involved in many important biological processes, such as cancer initiation, progression, and metastasis; hence, they are indicative of potential diagnostic biomarkers. Here, we demonstrate a new label free and sensitive electrochemiluminescent (ECL) sensing strategy for protease and nuclease assays that utilize target-triggered desorption of programmable polyelectrolyte films assembled on graphite-like carbon nitride (g-C3N4) film to regulate the diffusion flux of a coreactant. Furthermore, we have built Boolean logic gates OR and AND into the polyelectrolyte films, capable of simultaneously sensing proteases and nucleases in a complicated system by breaking it into simple functions. The developed intelligent permeability controlled enzyme sensor may prove valuable in future medical diagnostics.

In this work, we report a novel electrochemical sensor for the label-free, real time and highly sensitive detection of antibody–antigen interactions based on concave gold nanocuboids (CAuNCs). In contrast to low-index facet gold nanoparticles (AuNPs) such as gold nanorods (AuNRs), the CAuNCs provide higher surface atoms with enhanced chemical activities, which can efficiently catalyse the oxidation reaction of amino groups on antibodies (anti-bovine IgG produced in rabbit). This leads to an obvious redox current response being observed in cyclic voltammetry (CV) measurements. Upon the introduction of an IgG antigen, a notable decrease of the anodic peak current was observed, which is attributed to the formation of an antigen–antibody complex between the IgG antigen and the antibody on the CAuNCs. The unique electrocatalytic property of the CAuNCs allows easy detection of the rabbit IgG antigen in a wide range of concentrations (from 10 to 200 ng mL−1), with a limit of detection (LOD) to 5 ng mL−1 (signal to noise ratio 3 (S/N = 3)) by using a CV method.

•Various shapes of Au–Ni nanoparticles were synthesized by changing halide anions.•Clustered globular nanoparticles showed superior electrocatalytic activity.•Portion of high indexed plane made difference in electrocatalytic activity.Gold–nickel (Au–Ni) bimetallic nanoparticles in various forms of clustered globular, polyhedral, platelet and prickly nanoparticles were synthesized. The effect of sodium lauryl sulfate (SLS) and the halide anions on the shape of the Au–Ni nanoparticles were systematically investigated. By testing the electrocatalytic performances of differently shaped Au–Ni nanoparticles under methanol and ethanol oxidation conditions, the optimum shape for catalysis was suggested.

•Recent progress on different strategies for plasmonic nanosensors is highlighted.•An applications-oriented perspective in plasmonic nanosensors is provided.•The advantages and disadvantages of current detection platforms are discussed.Based on the localized surface plasmon resonance (LSPR) of metallic nanoparticles, plasmonic nanosensors have emerged as a powerful tool for biosensing applications. Many detection schemes have been developed and the field is rapidly growing to incorporate new methodologies and applications. Amidst all the ongoing research efforts, one common factor remains a key driving force: continued improvement of high-sensitivity detection. Although there are many excellent reviews available that describe the general progress of LSPR-based plasmonic biosensors, there has been limited attention to strategies for improving the sensitivity of plasmonic nanosensors. Recognizing the importance of this subject, this review highlights recent progress on different strategies used for improving the sensitivity of plasmonic nanosensors. These strategies are classified into the following three categories based on their different sensing mechanisms: (1) sensing based on target-induced local refractive index changes, (2) colorimetric sensing based on LSPR coupling, and (3) amplification of detection sensitivity based on nanoparticle growth. The basic principles and cutting-edge examples are provided for each kind of strategy, collectively forming a unifying framework to view the latest attempts to improve the sensitivity of nanoplasmonic sensors. Future trends for the fabrication of improved plasmonic nanosensors are also discussed.Figure optionsDownload full-size imageDownload high-quality image (135 K)Download as PowerPoint slide

We report the synthesis of uniform triangular gold nanoplates by a modified seeded growth method. The concentration of cetyltrimethylammonium bromide (CTAB) in the growth solution and the time interval between multiple steps of growth were important factors which determined the formation of uniform triangular Au nanoplates. In addition, by further isotropic overgrowth, the thickness of triangular Au nanoplates can be finely tuned within a wide range of 10–80 nm, which at present remains a challenge using conventional seeded growth.

Hierarchical metal nanostructures have attracted increasing interest due to their unique morphology-dependent properties. Here, we introduce a new and efficient method to synthesize hierarchical gold nanostructures in different shapes using the covalently capped seed-mediated growth approach.

Two-dimensional graphite-like carbon nitride nanosheets (g-C3N4 NSs) were hybridized with gold nanoparticles (Au NPs) to construct an electrochemiluminescence (ECL) immunosensor. The prepared Au NP-functionalized g-C3N4 NS nanohybrids (Au-g-C3N4 NHs) exhibit strong and stable cathodic ECL activity compared to g-C3N4 NSs due to the important roles of Au NPs in trapping and storing the electrons from the conduction band of g-C3N4 NSs, as well as preventing high energy electron-induced passivation of g-C3N4 NSs. On the basis of the improved ECL stability and ECL peak intensity of the Au-g-C3N4 NHs, a novel ECL immunosensor was developed to detect carcinoembryonic antigen (CEA) as a model target analyte. The ECL immunosensor has a sensitive response to CEA in a linear range of 0.02–80 ng mL–1 with a detection limit of 6.8 pg mL–1. Additionally, the proposed immunosensor shows high specificity, good reproducibility, and long-term stability.

We report a method to modify a silica capillary with poly(oligo(ethylene glycol)methacrylate) (POEGMA) and its performance for protein separation. We optimized the grafting density and thickness of the POEGMA film and investigated the effect of running buffer pH, ionic strength, separation voltage, and sample injection time. The POEGMA-coated capillary was successfully utilized for the separation of six model proteins. Under optimized conditions, the resolution was found to be much better than a bare capillary, and even better than a widely used, commercially available PEG-modified capillary.

A microfluidic chip integrated with pneumatically controlled valves was developed for multiplexed biomolecular detection via localized surface plasmonic resonance (LSPR) of single gold nanorod. The cost-effective microfluidic chip was assembled by polydimethylsiloxane layers and glass substrates with a precisely controlled thickness. The thin and flat microfluidic chip fitted the narrow space of dark-field microscopy and enabled the recording of single-nanoparticle LSPR responses. Aptamer-antigen-antibody sandwiched detection scheme was utilized to enhance the LSPR responses for label-free biomolecular detection. This microfluidic chip successfully demonstrated the multiplexed detection of three independent analytes (PSA, IgE, and thrombin).

The common drawbacks of current colorimetric sensors using gold nanoparticle aggregation is its relatively low sensitivity and narrow dynamic range, which restrict their application in real sample analysis when competing with other analytical techniques such as fluorescence and chemiluminescence. In this article, we demonstrate a novel strategy to construct colorimetric sensors based on gold nanoparticle aggregation. Unlike the conventional colorimetric sensors which cause the formation of large nanoparticle aggregates, in our strategy, dimers are selectively formed upon target binding, which results in significantly improved long-term stability and a more than 2 orders of magnitude wider dynamic range of detection than that of the conventional colorimetric sensors. In addition, a strategy to minimize the interparticle gap through the formation of a Y-shaped DNA duplex enables to increase the limit of detection by 10 000 times. The analytical figures of merit of the proposed sensor are comparable to those of the fluorescence-based sensors.

Gold nanoparticles have attracted considerable attention owing to their appealing plasmonic properties that have found applications in sensing, imaging, and energy harvesting. In the present article, we report the synthesis of anisotropic concave Au nanocuboids using a seeded growth method controlled by a seed concentration. Unlike conventional nonconcave counterparts which typically present two fundamental plasmonic modes (transverse and longitudinal modes), our experimental measurements and theoretical analysis show that the anisotropic concave Au nanocuboid has three plasmonic resonances. Theoretical calculations based on a finite element method confirm that the third resonance is a transverse “edge” mode, which is enhanced by the sharpened edges of the concave surfaces. This third resonance is found to be separated from the conventional broad transverse mode band. Because of the separation of the resonance mode, the quality-factor of the original transverse mode shows nearly a 3-fold enhancement.Keywords: anisotropic; concave; gold nanoparticles; high-index facets; plasmonic;

Here we report the template-free growth of hierarchical MnO2 spheres on indium tin oxide by electrodeposition for the first time. The structural evolution and growth mechanism of MnO2 was carefully investigated. The hierarchical MnO2 showed mesoporous structure and good biocompatibility for the immobilization of glucose oxidase (GOx). The bioconjugate of a GOx/MnO2-modified electrode was successfully employed for the mediatorless biosensing of glucose.

We report a novel composite material of hierarchically structured Mn3O4 grown on three-dimensional graphene foam (3DGF). This hierarchical Mn3O4/3DGF composite was fabricated as a flexible and freestanding biosensor for nonenzymatic determination of glucose and H2O2, significant analytes in health care and food industry. The Mn3O4/3DGF-based biosensor achieved high sensitivity, large linear range and low detection limit for the detection of both analytes, due to the synergistic effects of the two materials, which combines the high electrocatalytic activity of the nanostructured Mn3O4 network, and high conductivity and large surface area of 3DGF. This enzymeless biosensor also exhibited excellent performance for real-time detection of glucose and H2O2 in serum and food samples.

We have demonstrated a novel method for the preparation of a fluorescence-based pH sensor by combining the plasmon resonance band of Ag core and pH sensitive dye (HPTS). A thickness-variable silica shell is placed between Ag core and HPTS dye to achieve the maximum fluorescence enhancement. At the shell thickness of 8 nm, the fluorescence intensity increases 4 and 9 times when the sensor is excited at 405 and 455 nm, respectively. At the same time, the fluorescence intensity shows a good sensitivity toward pH value in the range of 5–9, and the ratio of emission intensity at 513 nm excited at 455 nm to that excited at 405 nm versus the pH value in the range of 5–9 is determined. It is believed that the present pH sensor has the potential for determining pH real time in the biological sample.Keywords: Ag nanoparticle; core−shell; fluorescence enhancement; HPTS; pH sensor; plasmon resonance;

We introduce gold nanorods (GNRs) decoration on NaYF4:Yb/Tm upconversion nanocrystals (UCNCs) by functionalizing the UCNCs with polyamidoamine generation 1 (PAMAM G1) dendrimer, followed by a single-step seed-mediated growth of long-range GNRs to enhance “biological window” upconversion emission. The up-conversion emission of GNR-decorated UCNCs can be enhanced beyond the level typically obtainable using shell-like structures up to 27-fold enhancement. Also, the enhancement can be tuned at different wavelength regions by varying the GNR aspect ratio. The GNR-decorated UCNC is further modified with 2-thiouracil for nonenzymatic detection of uric acid, revealing a detection limit as 1 pM.Keywords: biosensor; fluorescence enhancements; gold nanorods; PAMAM; upconversion nanocrystals;

We introduce a novel solid-phase colorimetric sensor facilely fabricated by loading unmodified gold nanoparticles into poly(oligo(ethylene glycol)methacrylate) (POEGMA) brushes grown on glass. Our work reports the first synergistic combination of metallic nanoparticles acting as a colorimetric sensing module with a nonfouling polymer matrix acting both as a nonrigid scaffold and a screen to reduce interference from nontarget molecules. In addition, as the nanocomposite is formed on a transparent substrate, solid-phase detection can be performed in the same manner as in the solution-phase. We demonstrate the use of this unique platform for label-free lead detection based on the release of gold nanoparticles from the polymer brush upon exposure to lead ions. An ultralow limit-of-detection of 25 pM (S/N = 3) and a dynamic range of 100 pM to 100 nM (R2 = 0.987) are achieved. Furthermore, the detection is up to 1000-fold more selective to lead over other common heavy metal ions.

We report a novel, simple strategy to efficiently enhance the fluorescence of metal-coated up-conversion nanoparticles (UCNPs), NaYF4:Yb,Er/Tm. The UCNPs are functionalized with a polyamidoamine generation 1 (PAMAM G1) dendrimer, followed by a continuous growth of gold (Au) or silver (Ag) nanoshells to selectively enhance the up-converted green, violet and blue emissions (>20 fold).

The physical immobilization of antibodies via spot-drying on polymer brush, poly(oligo(ethylene glycol) methacrylate) (POEGMA), was investigated by employing immunoglobulin G (IgG). Fluorescence measurements across a wide range of brush thicknesses from ∼6 to 102 nm interestingly revealed that the protein loading capacity of the brush did not linearly increase with thickness. With direct visual evidence provided by tapping mode atomic force microscopy (TM-AFM) we found that, at higher thicknesses, antibodies do not infiltrate into brush but instead embed at the sub-surface. By correlating our results with an existing theoretical model, which takes into account several critical size scales associated with free energy, we demonstrate for the first time a systematic methodology which can be employed to determine optimal conditions for maximized protein loading on the brush polymer. The optimal thickness for maximum IgG loading with good retention was found to be ∼62 nm, much lower than the maximum thickness used in this study (∼102 nm). Our results particularly provide insight on how size factors govern the organization of physically-immobilized proteins in polymer brushes, discouraging the simplistic belief that higher brush thickness always lead to increased protein loading due to higher degree of infiltration and eventually allowing a more precise control over the physical-immobilization process.

We report a new strategy for shape control over the synthesis of gold nanoparticles (AuNPs) by using a photoresponsive surfactant based on a modified seed growth method. Owing to photoresponsive properties of the azo group, the designed surfactant, N1,N3,N5-tris[(4′-azobenzene-4-sulphonic acid)phenyl]benzene-1,3,5-tricarboxamide, exhibits a distinctive molecular configuration under light leading to different growth processes of AuNPs. As a result, the blackberry-like, spherical AuNPs and multilayered Au plates were successfully prepared in high yield under visible and UV light. The size and morphological control of Au nanocrystals are described and the synthesized Au nanocrystals are evaluated for SERS applications.

We introduce a facile strategy to obtain dense 3-dimensional assembly of non-functionalized gold nanoparticles into unmodified, end-tethered poly(oligo(ethylene glycol) methacrylate) bottle brushes of high grafting densities. Referred to as ‘in-stacking’, we present its mechanism based on evidence from UV-vis absorbance, AFM and FESEM.

Here we demonstrate a polysaccharide hydrogel reinforced with finely dispersed single-walled carbon nanotubes (SWNTs) using biocompatible dispersants O-carboxymethylchitosan (OC) and chondroitin sulfate A (CS-A) as a structural support. Both of the dispersants can disperse SWNTs in aqueous solutions and hydrogel matrix as individual tubes or small bundles. Additionally, we have found that compressive modulus and strain of the hydrogels reinforced with SWNTs were enhanced as much as two times by the addition of a few weight percent of SWNTs. Moreover, the SWNT-incorporated hydrogels exhibited lower impedance and higher charge capacity than the alginate/dispersant hydrogel without SWNTs. The OC and the CS-A demonstrated much higher reinforcing enhancement than a commercially available dispersant, sodium dodecyl sulfate. Combined with the experimental data on the mechanical and electrical properties, the biocompatibility of OC and CS-A can provide the possibility of biomedical application of the SWNT-reinforced hydrogels.Keywords: alginate; biocompatibility; chondroitin sulfate A; O-carboxymethylchitosan; reinforced hydrogel; SWNT;

Herein we demonstrate a sensitive approach for protein detection based on peak shifts of localized surface plasmon resonance (LSPR) induced by aptamer–antigen–antibody sandwich structures. The applicability of the proposed method is demonstrated using human α-thrombin as a model analyte. While the binding of thrombin to its specific receptor, thrombin binding aptamer (TBA) modified on Au nanorods (AuNRs), causes a measurable LSPR shift, a subsequent binding of an anti-thrombin antibody to the captured thrombin can exhibit a nearly 150% amplification in the LSPR response. This enhanced signal essentially leads to an improvement of limit of detection (LOD) by more than one order of magnitude. In addition, the use of TBA as thrombin recognition units makes the biosensor reusable. The feasibility of the proposed method was further exploited by the detection of thrombin in human serum, opening the possibility of a real application for diagnostics and medical investigations.Highlights► The sandwich complex enhanced the LSPR peak shift more than 150%. ► The use of DNA aptamers as thrombin capture units makes the sensor reusable. ► Calibration curve and sample detection were achieved by a single nanoparticle. ► An averaged LOD of 1.6 pM was achieved for thrombin detection.

A label-free electrochemical immunosensor for the detection of neutrophil gelatinase-associated lipocalin (NGAL) is developed by the immobilization of rabbit polygonal lipocalin-2 antibody on gold nanoparticles attached on generation-1polyamidoamine (PAMAM) dendrimer (LA2/AuNPs/PAMAM)-modified gold electrode. The modification procedure was characterized by UV–vis, surface enhanced Raman spectroscopy and field-emission scanning electron microscopy techniques. The detection of NGAL is based on the enhancement of oxidation current on the modified electrodes upon the antigen–antibody interaction. The electrochemical immunosensor exhibited high sensitivity (1 ng mL−1 (280 pM) based on the signal-to-noise ratio 3), wide linear range (50–250 ng mL−1) and long-term stability. The reliability of the developed immunosensor was investigated by the detection of NGAL in both blood serum and urine samples.Highlights► A novel and simple label-free electrochemical immunosensor for the ultrasensitive detection of NGAL is developed. ► The LA2/AuNPs immunoelectrode is found to detect NGAL in the concentration range of 50–250 ng mL−1 with a low detection limit of 1 ng mL−1 (280 pM; based on S/N = 3). ► The developed immunosensor has been proved by the satisfactory results of the usage to determine NGAL in both blood serum and urine samples.

This paper reports a simple, one-step, template-free surface assisted growth of crystalline branched-like Au nanoparticles (three-dimensional (3-D) growth with more than 12 tips) with high yield and good size monodispersity at room temperature. The size of the Au branched nanocrystals could be tuned by controlling the composition of the starting reaction mixture (growth solution). The key surface growth strategy was to use a 1,6-hexanedithiol (HDT) monolayer-modified electrode immersed into growth solution to confine the growth of the branched Au nanocrystals on their surface. Time-course measurements by field emission-scanning electron microscopy (FESEM) were used to follow the reaction progress and the evolution of the branched-like nanocrystal shape. The Au nanocrystals exhibited strong surface enhanced effects which were utilized in the design of an efficient, stable, and Raman-active tag for biosensors, and electrocatalytic applications.

Orientation sensors require the monitoring of polarization-dependent surface plasmons of single nanoparticles. Herein, we present both the longitudinal and transverse surface plasmonic resonance from a single gold nanorod (AuNR) using conventional dark-field microscopy. The relative peak intensities of the transverse and longitudinal surface plasmons of a single AuNR can be successfully tuned by polarized excitation, which is an important step towards the use of transverse plasmon resonance of single AuNRs without photo-induced reshaping of nanoparticles. More interestingly, compared with AuNRs with small diameters, unique optical properties from AuNRs with diameters greater than 30 nm are revealed. As a result, optical images with different colors, rainbow nanoparticles (sea green, brown, red, yellow and green), depending on the polarization angle, can be revealed by a single AuNR. This result holds great promise for polarization-controlled colorimetric nanomaterials and single particle tracers in living cells and microfluidic flows.

A new strategy of electrogen immobilization was developed to construct a conductive artificial biofilm (CAB) on an anode of a microbial fuel cell (MFC). The MFCs equipped with an optimized CAB exhibited an eleven fold increase in power output compared with natural biofilms.

We demonstrate plasmonic aptasensors that allow a single nanoparticle (NP) to generate a calibration curve and to detect analytes. The proposed reusable aptasensors have significant advantages over conventional single-NP based assays in terms of sensitivity and reproducibility.

Here, we present a mean to expand the use of individual metallic nanoparticles to two-dimensional plasmonic nanoarrays. An optical detection platform to track down localized surface plasmon resonance (LSPR) signals of individual nanoparticles on substrates was built for the application of plasmonic nanoarrays. A pseudoimage of nanoparticles on a substrate was reconstructed from their scattering spectra obtained by scanning a user-defined area. The spectral and spatial resolutions of the system were also discussed in detail. Most importantly, we present a method to normalize the localized surface plasmon resonance from geometrically different nanoparticles. After normalization, plasmonic responses from different particles become highly consistent, creating well-fitted dose−response curves of both surrounding refractive index changes and receptor−analyte binding to the surface of individual nanoparticles. Finally, the proof-of-concept system for plasmonic nanoarray detection is demonstrated by the measurement of the aptamer−thrombin binding event.

Herein, a simple and effective approach is reported for the in situ generation and regeneration of a Au nanorod (AuNR) monolayer inside a glass/silica-based, closed-surface flow channel. The density of the AuNR monolayer in the flow channel can be easily modified by varying the concentration of the AuNR and the cetyltrimethylammonium bromide as well as the incubation time. The fabricated AuNR monolayer in the flow channels was stable under harsh conditions, such as in extreme pH, organic solvents and at a fast flow rate. In addition, the flow channel could be reused by removing the immobilized AuNRs via the injection of diluted aqua regia or potassium iodide; the AuNR monolayer can subsequently be regenerated. The AuNRs in the closed flow channel were further exploited as a label-free detection method for a clinical biomarker, neutrophil gelatinase-associated lipocalin (NGAL), based on single-nanoparticle plasmonic assay. The corresponding limit of detection for NGAL was measured to be 8.5 ng mL−1 (∼340 pM) based on a signal-to-noise ratio of 3. The estimated recovery of NGAL in human serum and urine was higher than 80%, which indicates that this technique could potentially be used for the diagnosis of acute kidney injury.

A novel method is developed to fabricate the polypyrrole (PPy) and graphene thin films on electrodes by electrochemical polymerization of pyrrole with graphene oxide (GO) as a dopant, followed by electrochemical reduction of GO in the composite film. The composite of PPy and electrochemically reduced graphene oxide (eRGO)-modified electrode is highly sensitive and selective toward the detection of dopamine (DA) in the presence of high concentrations of ascorbic acid (AA) and uric acid (UA). The sensing performance of the PPy/eRGO-modified electrode is investigated by differential pulse voltammetry (DPV), revealing a linear range of 0.1–150 μM with a detection limit of 23 nM (S/N = 3). The practical application of the PPy/eRGO-modified electrode is successfully demonstrated for DA determination in human blood serum.

We describe the development of a simple and highly sensitive electrochemical (amperometric) sensing of bilirubin based on bilirubin oxidase (BOx) incorporated into the gold nanoparticles (AuNPs). This nanoelectrode platform with self-assembled enzyme is highly sensitive toward the electrochemical oxidation of bilirubin and increased the bilirubin concentration linearly from 1 to 5000 μM with a correlation coefficient of 0.9960, and an apparent Michaelis constant (KM,app) of 44 ± 0.4 μM. Using an amperometric method, the detection limit for bilirubin at the enzyme-modified electrode was 1.4 nM (signal-to-noise ratio = 3). The modified electrode retained a stable response for 2 days while losing only ca. 3.4% of its initial sensitivity during a 10 days storage period in 0.2 M phosphate buffer solution (pH = 8.4) at ≤4 °C. The practical application of the modified electrode was demonstrated by measuring the concentration of bilirubin in blood serum sample.Highlights► The enzyme incorporated AuNPs on sol–gel film electrode is highly sensitive toward the electro-oxidation of bilirubin. ► The electrocatalytic oxidation current of bilirubin increased linearly from 1 to 5000 μM at enzyme-modified electrode with a correlation coefficient of 0.9960. ► Using an amperometric method, the detection limit of bilirubin was found to be 1.4 nM (S/N = 3). ► The practical application of the modified electrode was demonstrated by measuring the concentration of bilirubin in blood serum.

A novel one-dimensional hierarchically structured TiO2 (1DHS TiO2) was synthesized by a solvothermal method using multiwalled carbon nanotubes (MWCNTs) as a template and evaluated for the immobilization of protein and biosensing applications. Characterization studies showed that the 1DHS TiO2 possessed an anatase crystalline structure and a large surface area with narrow pore size distribution. Fast direct electron transfer was observed for glucose oxidase (GOx) immobilized on the 1DHS TiO2, and excellent electrocatalytic performance for glucose detection can be obtained without a mediator. The glucose sensor based on the GOx/1DHS TiO2-modified electrode had a high sensitivity of 9.90 μA mM–1 cm–2 and a low detection limit of 1.29 μM. The fabricated biosensor displayed good selectivity and long-term stability, indicating that the novel structured TiO2 is a promising material for the immobilization of biomolecules and the fabrication of third-generation biosensors.Keywords: biosensor; direct electrochemistry; glucose oxidase; hierarchical TiO2; solvothermal synthesis

We describe the development of a highly stable and sensitive glucose biosensor based on the nanohybrid materials derived from gold nanoparticles (AuNPs) and multi-walled carbon nanotubes (MWCNT). The biosensing platform was developed by using layer-by-layer (LBL) self-assembly of the nanohybrid materials and the enzyme glucose oxidase (GOx). A high density of AuNPs and MWCNT nanocomposite materials were constructed by alternate self assembly of thiol functionalized MWCNTs and AuNPs, followed by chemisoption of GOx. The surface morphology of multilayered AuNPs/MWCNT structure was characterized by field emission-scanning electron microscope (FE-SEM), and the surface coverage of AuNPs was investigated by cyclic voltammetry (CV), showing that 5 layers of assembly achieves the maximum particle density on electrode. The immobilization of GOx was monitored by electrochemical impedance spectroscopy (EIS). CV and amperometry methods were used to study the electrochemical oxidation of glucose at physiological pH 7.4. The Au electrode modified with five layers of AuNPs/MWCNT composites and GOx exhibited an excellent electrocatalytic activity towards oxidation of glucose, which presents a wide liner range from 20 μM to 10 mM, with a sensitivity of 19.27 μA mM−1 cm−2. The detection limit of present modified electrode was found to be 2.3 μM (S/N = 3). In addition, the resulting biosensor showed a faster amperometric current response (within 3 s) and low apparent Michaelis–Menten constant (Kmapp). Our present study shows that the high density of AuNPs decorated MWCNT is a promising nanohybrid material for the construction of enzyme based electrochemical biosensors.

In this work, we present a simple and effective method to fabricate distance-controllable, Au nanorod (AuNR) chips thorough electrostatic assembly. Cetyltrimethylammonium bromide (CTAB)-capped AuNRs were immobilized on a hydroxyl-functionalized glass substrate by immersion of the glass into AuNR-suspension. The electrostatic surfacial assembly of AuNRs offers significant advantages over conventional thiol-induced chemistry, i.e., direct control of self-assembly of AuNRs, easy fabrication in ambient environment and most importantly, broad range of tunable inter-particle distance, ranging from 0.25 to 10 μm. The mechanism of time-dependant deposition process of AuNRs was described via competitive bindings of AuNRs and free CTAB molecules in AuNR-suspension. In addition, the electrostatically anchored AuNRs on a glass substrate provide sufficient stability under harsh experimental conditions with flow of basic/acidic solutions and organic solvents with different polarity. The feasibility of the AuNR-chips fabricated by the proposed method for single-nanoparticle plasmonic biosensors was demonstrated by the plasmonic measurement of aptamer–thrombin binding event. The corresponding limit of detection of thrombin molecule was found to be ∼278 pM based on the signal to noise ratio of 4.

We report the synthesis of cetyltrimethylammonium bromide (CTAB) assisted seed mediated growth of highly pure and monodispersed quasispherical gold nanoparticles (QAuNPs) and their self-assembly on the silica/glass substrates. The seed-mediated growth approach was modified to prepare size-tunable monodispersed QAuNPs with sizes ranging from 20 to 150 nm. The larger, more uniform seeds and lower CTAB concentration resulted in the formation of relatively large QAuNPs with improved monodispersity (relative standard deviation (RSD) of ∼5–8%) and high purity in their shapes. In addition, CATB-capped QAuNPs can be spontaneously assembled into closely packed and highly aligned superstructures with well-defined mutillayers (two to six layers) on silica substrates. Furthermore, CATB-capped QAuNPs can easily construct density-controllable QAuNP chips by electrostatic self-assembly, showing their promising applications for single-nanoparticle plasmonic sensors.

The surface of neural electrodes was modified with multilayered, polypyrrole (PPy)-coated, multiwalled carbon nanotubes (MWCNTs) via the layer-by-layer fabrication method. The modified electrode with PPy-coated MWCNTs exhibited a significant improvement over conventional Au electrodes and PPy-coated electrodes with respect to the electrical properties based on charge storage capacity (660 times larger), impedance (5 times lower), and electrochemical stability (3 times more stable). Positive results from the biocompatibility tests conducted on PC12 cells and RAW 264.7 further suggested that our multilayered, PPy-coated MWCNT was an excellent candidate for the surface modification of neural electrodes.

Three-dimensional gold nanoarchitecture was fabricated by layer-by-layer (LbL) deposition of gold nanoparticles (AuNPs) and multiwalled carbon nanotubes (MWCNTs) on a glass substrate for a highly sensitive plasmonic biosensor using a conventional UV−vis instrument. Carboxyl-functionalized MWCNTs were reacted with 3-mercaptopropyltriethoxysilane (MPTES) to introduce multiple thiol groups onto MWCNTs. A self-assembled monolayer (SAM) of AuNPs on a glass chip was sequentially dipped into MPTES-functionalized MWCNTs (MWCNT-Si-SH) and AuNPs to form multilayers of AuNPs on MWCNTs. Such three-dimensionally assembled AuNPs provided a large surface area and multiple binding sites within a few steps of modification and microporous structures of multilayered MWCNTs to allow a high accessibility of target molecules. It was shown that the bulk refractive index (RI) sensitivity of these multilayered AuNPs (three-dimensional chip) appeared to be 5.6 times better than that of a monolayer of AuNPs on a glass chip (two-dimensional chip). The three-dimensional chips were further used for a biomolecular binding study, showing a detection limit as low as 0.5 nM for streptavidin and 3.33 nM for anti-human serum albumin (HSA), both of which were ∼20 times higher than the sensitivity of the two-dimensional chips.

The effect of ionic strength as well as surfactant concentration on the surface assembly of cetyltrimethylammonium bromide (CTAB)-capped gold nanorods (GNRs) has been studied. Glass substrates were modified to yield a net negative charge through electrostatic coating of polystyrenesulfonate (PSS) over a self-assembled monolayer (SAM) of positively charged aminopropyltriethoxysilane (APTS). The substrates were then fully immersed in GNR solutions at different CTAB concentrations and ionic strengths. Under slightly excess CTAB concentrations, it was observed that the density of GNRs immobilized on a substrate was predictably tunable through the adjustment of NaCl concentration over a wide range. Motivated by the experimental observation, we hypothesize that electrostatic shielding of charges around the GNRs affects the density of GNR immobilization. This model ultimately explains that at moderate to high CTAB concentrations a second electrostatic shielding effect contributed by excess CTAB molecules occurs, resulting in a parabolic trend of nanorod surface density when ionic strength is continually increased. In contrast, at a low CTAB concentration, the effect of ionic strength becomes much less significant due to insufficient CTAB molecules to provide for the second electrostatic shielding effect. The tunability of electrostatic-based surface assembly of GNRs enables the attainment of a dense surface assembly of nanorods without significant removal of CTAB or any other substituted stabilizing agent, both of which could compromise the stability and morphology of GNRs in solution. An additional study performed to investigate the robustness of such electrostatic-based surface assembly also proved its reliability to be used as biosensing platforms.

We report a novel composite material of hierarchically structured Mn3O4 grown on three-dimensional graphene foam (3DGF). This hierarchical Mn3O4/3DGF composite was fabricated as a flexible and freestanding biosensor for nonenzymatic determination of glucose and H2O2, significant analytes in health care and food industry. The Mn3O4/3DGF-based biosensor achieved high sensitivity, large linear range and low detection limit for the detection of both analytes, due to the synergistic effects of the two materials, which combines the high electrocatalytic activity of the nanostructured Mn3O4 network, and high conductivity and large surface area of 3DGF. This enzymeless biosensor also exhibited excellent performance for real-time detection of glucose and H2O2 in serum and food samples.

Correction for ‘Controlled size and morphology, and phase transition of YF3:Yb3+,Er3+ and YOF:Yb3+,Er3+ nanocrystals for fine color tuning’ by Yongsheng Zhu et al., J. Mater. Chem. C, 2016, DOI: 10.1039/c5tc03473f.

A single-nanoparticle plasmonic sensor for the sensitive detection of gas molecules (NO2) has been constructed. Taking advantage of active molecular plasmonics, the analyte selectively triggers a measurable spectral shift of ferrocene-modified single gold nanorods.

A novel permeability gate-based electrochemiluminescent (ECL) aptasensor has been constructed by utilizing target-responsive polyelectrolyte–aptamer film deposited on the solid-state ECL electrode to control the rate of diffusion of a coreactant that triggers the ECL.

This paper reports a simple, one-step, template-free surface assisted growth of crystalline branched-like Au nanoparticles (three-dimensional (3-D) growth with more than 12 tips) with high yield and good size monodispersity at room temperature. The size of the Au branched nanocrystals could be tuned by controlling the composition of the starting reaction mixture (growth solution). The key surface growth strategy was to use a 1,6-hexanedithiol (HDT) monolayer-modified electrode immersed into growth solution to confine the growth of the branched Au nanocrystals on their surface. Time-course measurements by field emission-scanning electron microscopy (FESEM) were used to follow the reaction progress and the evolution of the branched-like nanocrystal shape. The Au nanocrystals exhibited strong surface enhanced effects which were utilized in the design of an efficient, stable, and Raman-active tag for biosensors, and electrocatalytic applications.

Here we report the template-free growth of hierarchical MnO2 spheres on indium tin oxide by electrodeposition for the first time. The structural evolution and growth mechanism of MnO2 was carefully investigated. The hierarchical MnO2 showed mesoporous structure and good biocompatibility for the immobilization of glucose oxidase (GOx). The bioconjugate of a GOx/MnO2-modified electrode was successfully employed for the mediatorless biosensing of glucose.

We demonstrate plasmonic aptasensors that allow a single nanoparticle (NP) to generate a calibration curve and to detect analytes. The proposed reusable aptasensors have significant advantages over conventional single-NP based assays in terms of sensitivity and reproducibility.

Lanthanide rare-earth (RE) based upconversion nanocrystals (UCNCs) have the ability to generate visible emission as well as a wide range of applications under near-infrared excitation. However, each lanthanide ion has a unique set of energy levels and generally exhibits a set of sharp emission peaks. Nowadays, it is very important to finely tune the upconversion (UC) properties through controlling the particle size, crystalline phase and shape of UCNCs. Herein, we reported the systematic synthesis and fine control of monodisperse rare-earth doped fluoride and oxyfluoride nanocrystals (NCs) in the same reaction system. When the ratios of oleic acid (OA) to oleylamine (OM) decreased from 4:1 to 3:8, the shapes of NCs changed from rhombic nanoplates to small spherical nanoparticles (~2 nm), while the crystalline phases changed from the orthorhombic phase (YF3) to the tetragonal phase (YOF). Furthermore, it is interesting to observe that the emission color changed from green to red with the transformation of both the crystalline phase and shape, which can broaden the applications of rare-earth based nanomaterials ranging from displays to bioimaging.

A new strategy of electrogen immobilization was developed to construct a conductive artificial biofilm (CAB) on an anode of a microbial fuel cell (MFC). The MFCs equipped with an optimized CAB exhibited an eleven fold increase in power output compared with natural biofilms.