Transition metal ions, such as those generated through MoS2 material, possess an intrinsic fluorescence quenching property towards organic dye molecules; thus, they can be used to construct biosensors as quenchers. However, we found that the conventional bulk MoS2 blocks the view of fluorescence imaging, and is incapable of tracing and visualizing mucin 1-overexpression cancer cells. Herein, a FAM fluorophore-labeled ssDNA fluorescent probe (P0-FAM) stacked on the surface of MoS2 quantum dots (QDs) was used to construct a MoS2 QDs–P0-FAM biosensor. MoS2 QDs exhibit a high fluorescence quenching ability towards fluorescent dyes, possess large specific surface area and a large number of active sites to adsorb and quench more fluorescent probes, promoting sensitivity between quenching and the recovery signal. In addition, the lighter color of unstack-MoS2 QDs is beneficial to define the location of cancer cells compared to MoS2 nanosheets. The novel MoS2 QDs-based biosensor demonstrates high sensitivity to MUC1 with a detection limit of 0.5 nM, and may become an important tool toward the detection of cancer cells.

Electrochemiluminescence (ECL) property of nitroolefin-based fluorescein was investigated and reported for the first time. Its ECL behaviors in acetonitrile (CH3CN) system and aqueous system were studied, respectively. Results indicated that nitroolefin-based fluorescein showed reversible reduction peaks on cycling voltammetric (CV) spectrum and produced ECL emission with the presence of benzoyl peroxide (BPO) as a coreactant in CH3CN solution. Reduction potential peaks of the substance can be observed in water solution in CV, and the intensity of ECL emission is much lower in water than that of in CH3CN solution. However, the ECL property of nitroolefin-based fluorescein can be used for the detection of cysteine (Cys) by using potassium persulfate (K2S2O8) as coreactant in aqueous solution. Under optimum conditions, the ECL intensity has a linear relationship with the concentration of cysteine in the range of 10−9 to 10−8 mol L−1 and a detection limit of 4.2 × 10−10 mol L−1. It has a lower detection limit than the fluorescence method. Our investigation demonstrated that the proposed method provides an elegant platform for fabrication of new generation of biosensors with ultrahighsensitivity, and might have potentially broad applications in amino acids diagnostics and bioassay.

•FRET biosensor using NaEuF4 NPs and Au@Ag2S NPs as the energy donor–acceptor pair.•Study suitable distance between donor and acceptor to obtain efficient FRET system.•Ultrasensitively detect target DNA with a detection limit of 32 aM.The work investigates a new fluorescence resonance energy transfer (FRET) system using NaEuF4 nanoparticles (NPs) and Au@Ag2S NPs as the energy donor–acceptor pair for the first time. The NaEuF4/Au@Ag2S NPs-based FRET DNA sensor was constructed with NaEuF4 NPs as the fluorescence (FL) donor and Au@Ag2S core−shell NPs as FL acceptor. In order to find the matching energy acceptor, the amount of AgNO3 and Na2S were controlled in the synthesis process to overlap the absorption spectrum of energy acceptor with the emission spectrum of energy donors. The sensitivity of FRET-based DNA sensor can be enhanced and the self-absorption of ligand as well as the background of signals can be decreased because of Eu3+ which owns large Stokes shifts and narrow emission bands due to f–f electronic transitions of 4f shell. We obtained the efficient FRET system by studying suitable distance between the donor and acceptor. Then the FRET-based DNA sensor was used for the design of specific and sensitive detection of target DNA and the quenching efficiency (ΔFL/F0, ΔFL=F−F0) of FL was logarithmically related to the concentration of the target DNA, ranging from 100 aM to 100 pM. We can realize an ultrasensitive detection of target DNA with a detection limit of 32 aM. This proposed method was feasible to analyse target DNA in real samples with satisfactory results.A new fluorescence resonance energy transfer (FRET) system using NaEuF4/Au@Ag2S NPs as the energy donor–acceptor pair was reported for the first time. Then the FRET-based DNA sensor was used for the sensitive detection of target DNA and its quenching efficiency (ΔFL/F0, ΔFL=F−F0) of FL was logarithmically related to the concentration of the target DNA, ranging from 100 aM to 100 pM, and an ultrasensitive detection of target DNA with a detection limit of 32 aM was obtained.

•A ECL sensor was assembled by rGO-BaYF5: Yb, Er prepared in situ hydrothermal.•ECL intensity of rGO-BaYF5: Yb, Er modified by AuNPs was enhanced 4-fold.•Immunosensor exhibited high selectivity to CEA with low detection limit.•The immunosensor was applied to a real sample (human serum samples).•The immunosensor has advantageous potential for future clinical analysis.We reported a novel ECL immunosensor for detection of carcinoembryonic antigen (CEA) based on the reduced graphene Oxide-BaYF5:Yb, Er (rGO-BaYF5:Yb, Er) nanocomposites. The rGO-BaYF5:Yb, Er nanocomposites, used as electrode luminescence materials, were prepared by in situ hydrothermal method, and characterized by TEM, XRD, UV–vis spectra, and upconversion fluorescence spectra. Further, poly (diallyldimethylammonium chloride) (PDDA), Au nanoparticles (AuNPs), and Anti-CEA were successively assembled on the surface of rGO-BaYF5:Yb, Er nanocomposites modified-electrode for fabricating ECL immunosensor. The results of the ECL measurements of CEA indicated that this novel ECL immunosensor exhibited high sensitive response to CEA in a linear range of 0.001–80 ng mL−1 with a low detection limit of 0.87 pg mL−1, good selectivity and satisfactory stability.

•The Au-F127 NPs offered a large and multifunctional surface for immobilization of anti-CEA.•Performance of immunosensor was evaluated by assemblied with Au-F127 NPs and anti-CEA.•The proposed immunosensor showed a wide liner response range with a low detection limit.Nanomaterial-based signal-amplification strategies hold a great promise in realizing sensitive biological detection. A simple label-free electrochemical immunosensor for sensitive detection of carcinoembryonic antigen (CEA) was developed by immobilizing anti-CEA antibodies onto the Au-F127 strawberry-like nanospheres modified glassy carbon electrode (Au-F127/GCE). The Au-F127 strawberry-like nanospheres offered a large surface and multifunctional substrate for the effective immobilization of anti-CEA and the existence of Au could accelerate electron transfer and make the electrochemical signal amplified. The Au-F127 nanocomposites and anti-CEA were characterized by transmission electron microscopy (TEM), polycrystalline electron diffraction ring pattern, ultra-violet visible (UV–vis) spectra and attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectra. Electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV) were employed to verify the stepwise assembly of the immunosensor and evaluated the analytical performance of the fabricated immunosensor, respectively. The immunosensor showed a wide liner response range between 0.01 and 80 ng mL−1 with a low detection limit of 0.24 pg mL−1 at a signal-to-noise (S/N) ratio of 3. Additionally, the proposed method was successfully applied to determine CEA in human serum samples with satisfactory results.

Chemiluminescence was used as an excitation light source to construct a universal photoelectrochemical platform based on Mn2+-doped NaYF4:Yb/Er upconversion nanoparticles, which greatly improves the electrochemiluminescence intensity and offers more stable cathodic signals compared to pure NaYF4:Yb/Er NPs. Here, we report for the first time the ECL behaviors of Mn2+-doped NaYF4:Yb/Er NPs, which were synthesized via a facile strategy. Mn2+ doping resulted in a 4-fold ECL intensity enhancement of NaYF4:Yb/Er. The characteristics of Mn2+-doped NaYF4:Yb/Er nanocomposites were obtained using transmission electron microscopy (TEM), energy dispersive X-ray spectrometer (EDS), and fluorescence spectra. After all the results had indicated that NaYF4:Yb/Er upconversion nanoparticles were successfully doped with Mn2+, the electrochemiluminescence platform was built. The as-prepared NaYF4:Yb/Er NPs were rendered water-soluble and then employed as ECL emitters for carcinoembryonic antigen (CEA) determination. The results indicated that the modified electrode can be used to determine CEA without interference from non-specific proteins, with a low detection limit of 5.2 pg mL−1. The biosensor can also be used for quantification of the CEA concentration in real samples.

Analysts are always interested in finding new functional nanomaterials and devices with good properties for electrochemical sensor applications. In this paper, hyperbranched polyester nanoparticles with carboxylic acid functional groups (HBPE–CA NPs) were synthesized and combined with chitosan wrapped around Au nanoparticles (CS–Au NPs) to prepare a novel and sensitive electrochemical immunosensor by adsorption of carcinoembryonic antibody (anti-CEA) on the (HBPE–CA)/CS–Au NPs modified glass carbon electrode (GCE). Under the optimized conditions, the proposed immunosensor displayed a good amperometric response to carcinoembryonic antigen (CEA). Moreover, based on the antibiofouling properties, the immunosensor could be used for the direct detection of CEA in whole blood, and exhibited a wide detection range (1–107 fg mL−1), and a low detection limit of 0.251 fg mL−1 (signal/noise = 3). Control experiments were also carried out by using ascorbic acid (AA), uric acid (UA), human immunoglobulin G (IgG), BSA and glucose in the absence of CEA. The good stability and repeatability of this immunosensor were also proven. Importantly, the results of the detection of clinical whole blood specimens with the proposed immunosensor showed good consistency with the data determined by enzyme-linked immunosorbent assay (ELISA) in serum samples. Furthermore, the developed immunosensor could provide a promising immunoassay strategy for clinical applications, since the values we measured in whole blood directly are likely closer to the real values.

In this work, three kinds of nanostructured silica–phytic acid (SiO2–PA) materials with diverse morphologies including spherical SiO2–PA (s-SiO2–PA), rod-like (r-SiO2–PA), and helical SiO2–PA (h-SiO2–PA) were prepared with the help of electrostatic interaction. The SiO2–PA nanomaterials with different morphologies were characterized by using transmission electron microscopy (TEM), Fourier transform infrared (FTIR), electrochemical impedance spectroscopy (EIS), and circular dichroism spectrum (CD). Diverse morphologies of SiO2–PA were used as electrode decorated materials to achieve a high efficiency for electrochemical dopamine (DA) detection. The laccase biosensors were fabricated by immobilizing different morphologies of SiO2–PA nanomaterials and laccase onto the glassy carbon electrode (GCE) surface, successively. Then the electrochemical responses of the different morphologies of nanostructured SiO2–PA nanomaterials to laccase were discussed. Results indicated that compared to laccase/s-SiO2–PA and laccase/r-SiO2–PA, the laccase/h-SiO2–PA-modified electrode showed the best electrochemical performances.

The development of materials for the ultra sensitive detection of biological species has received great attention. Here, a new electrochemical immunosensor for sensitive detection of tumor marker was reported. Polydopamine (PDA) coating was used to modify indium tin oxide (ITO) electrode for functionalized mesoporous silica nanoparticles immobilization. The carcinoembryonic antigen (CEA) was used as a model analyte. The capture anti-CEA was immobilized on functionalized mesoporous silica nanoparticles. The horseradish peroxidase (HRP)-labeled signal anti-CEA antibodies were used to conjugated with gold nanoparticles. After the sandwich immunoreaction, under optimized conditions, the proposed immunosensor showed a high sensitivity and a linear range of 0.01–40.0 ng/mL with a detection limit of 1.7 pg/mL. The assay results of clinical serum samples obtained by the immunosensor we proposed were in acceptable agreement with the reference values. The designed immunoassay system with ultrahigh sensitivity and efficient and economical, might have potentially broad applications in protein diagnostics and bioassay.

•Phosphonic acid-functionalized silica (SiO2-P) nanospheres were successfully prepared by the method of reverse microemulsion and electrostatic binding.•Biomimetic surface was provided by the prepared SiO2-P nanospheres that the entrapped xanthine oxidase (XOD) could preserve its bioactivity.•The XOD biosensor modified by SiO2-P nanospheres exhibited an excellent electrochemical behavior.A novel hypoxanthine biosensor fabricated by immobilizing the xanthine oxidase (XOD) onto the phosphonic acid-functionalized silica (SiO2-P) film on the surface of glassy carbon electrode (GCE) was designed and constructed in this work. A biomimetic platform was designed with the phosphonic acid-functionalized silica nanoparticles (SiO2-P NPs) synthesized by the method of reverse microemulsion and electrostatic binding. In such a platform, XOD was selected as model protein to fabricate hypoxanthine biosensor based on SiO2-P NPs. The nanocomposite was characterized with transmission electron microscopy (TEM), energy dispersive X-ray spectrometer (EDS) and electrochemical impedance spectroscopy (EIS). Based on the advantageous functions of SiO2-P NPs, the entrapped XOD could preserve its bioactivity and exhibited an excellent electrochemical behavior with a formal potential of −0.37 V in phosphate buffer solution (PBS, pH=7). Response studies to hypoxanthine were carried out using current–time response curve. The biosensor exhibited a wide linear response ranging from 1.00×10−6 to 2.61×10−4 M. The detection limit of 2.33×10−7 M at a signal-to-noise ratio of 3 was lower than that most reported previously. In addition, the electrode modified with XOD/(SiO2-P NPs) film also had a strong anti-interference ability in the presence of uric acid (UA) and ascorbic acid (AA). The assay results of hypoxanthine in fish samples were in a good agreement with the reference values.

In this case, the Au-F127 (triblock copolymer PEO106PPO70PEO106, PEO is short for polyethylene oxide and PPO is the abbreviation of polypropene oxide) hybrid hairy nanospheres were obtained by the redox reaction using pluronic F127 and HAuCl4 as precursor. A novel hemoglobin (Hb) biosensor was fabricated by immobilizing the Hb onto the Au-F127 film on the surface of glassy carbon electrode (GCE). The Au-F127 nanocomposites and Hb were characterized by transmission electron microscopy (TEM), polycrystalline electron diffraction ring pattern and ultra-violet visible spectra (UV–vis). UV–vis spectra suggested that Hb in the film could keep its native secondary structure. The performances of Hb/(Au-F127) on GCE were characterized with cyclic voltammetry (CV) and typical amperometric response (i–t) measurements. The immobilized Hb maintained its bioactivity and displayed an excellent electrochemical behavior with a formal potential of −339 mV. The resulting electrode showed an electrocatalytic activity to hydrogen peroxide (H2O2). The linear response range of the H2O2 biosensor was from 3.0 × 10−7 to 5.7 × 10−4 M with a low detection limit of 4.0 × 10−8 M.

Chemiluminescence was used as an excitation light source to construct a universal photoelectrochemical platform based on Mn2+-doped NaYF4:Yb/Er upconversion nanoparticles, which greatly improves the electrochemiluminescence intensity and offers more stable cathodic signals compared to pure NaYF4:Yb/Er NPs. Here, we report for the first time the ECL behaviors of Mn2+-doped NaYF4:Yb/Er NPs, which were synthesized via a facile strategy. Mn2+ doping resulted in a 4-fold ECL intensity enhancement of NaYF4:Yb/Er. The characteristics of Mn2+-doped NaYF4:Yb/Er nanocomposites were obtained using transmission electron microscopy (TEM), energy dispersive X-ray spectrometer (EDS), and fluorescence spectra. After all the results had indicated that NaYF4:Yb/Er upconversion nanoparticles were successfully doped with Mn2+, the electrochemiluminescence platform was built. The as-prepared NaYF4:Yb/Er NPs were rendered water-soluble and then employed as ECL emitters for carcinoembryonic antigen (CEA) determination. The results indicated that the modified electrode can be used to determine CEA without interference from non-specific proteins, with a low detection limit of 5.2 pg mL−1. The biosensor can also be used for quantification of the CEA concentration in real samples.