Enzymatic Biocatalytic Precipitation Research Articles

Dual-Mode Immunoassay Constructed by Water-Induced Perylene Diimide Supramolecular Self-Assembly and Enzymatic Biocatalytic Precipitation Strategy.

A water-induced electron-deficient dye, the supramolecule perylene diimide (PDI), has been identified recently. PDI possesses advantages such as easy reduction, nontoxicity, low cost, and simple preparation, making it a promising candidate for electrochemiluminescence (ECL) sensing platforms. In this study, a series of PDI supramolecular systems with morphological changes were prepared by utilizing water molecules to induce PDI self-assembly. This method improves the π-π stacking interactions between PDI molecules and effectively mitigates the aggregation-caused quenching (ACQ) effect on the luminous efficiency of the coplanar polycyclic aromatic hydrocarbon PDI. It is noteworthy that excellent ECL emission performance of the PDI supramolecular system was observed at -0.4 V. This low excitation potential aids in preserving antigen-antibody bioactivity and ensures accurate identification of the immune response. As a proof of concept, a dual-mode immunosensing platform for carcinoembryonic antigen (CEA) detection was constructed using an enzymatic biocatalytic precipitation (EBCP) strategy. The dual-mode immunosensor exhibited good detection performance in the concentration range of 0.001-80 ng·mL-1, presenting an advanced bioprotective analytical method for CEA detection.

Dual suppression amplification based on resonance energy transfer and enzymatic biocatalytic precipitation for IgG electrochemiluminescence ultrasensitive assay

Due to the necessity of ultrasensitive bioassays in life science, electrochemiluminescence (ECL) methodologies coupled with amplification strategies has drawn great attention recently. Herein, a versatile and robust dual suppression-based signal amplification strategy was proposed for IgG specifically ultrasensitive detection. A sandwich ECL sensor was constructed by employing Ru(bpy)32+ adsorbed on silica microspheres (Ru@SiO2) as luminophor. Fe3O4 nanoparticles (Fe3O4 NPs) were introduced on sensing platform through an antigen-antibody affinity, which played double roles. As an acceptor of resonance energy transfer (RET), Fe3O4 NPs remarkably quenched the ECL signal of Ru@SiO2. Meanwhile, Fe3O4 NPs, as a typical peroxidase-mimicking enzyme, catalyzed H2O2 to produce insoluble product based on enzymatic biocatalytic precipitation (BCP). As such, an efficient dual suppressive ECL platform has been achieved by the integration of ECL-RET and BCP techniques, which has been applied to ultrasensitively detect IgG with a linear range and limit of detection of 10 fg/mL to 1 μg/mL and 4.9 fg/mL, respectively. The new integrated system with RET and BCP may provide a potential promising in the development of highly efficient ECL systems for clinical diagnosis.

Hybridization Chain Reaction-Enhanced Biocatalytic Precipitation on Flower-like Bi2S3: Toward Organic Photoelectrochemical Transistor Aptasensing with High Transconductance.

Organic photoelectrochemical transistor (OPECT) bioanalysis has recently emerged as a promising avenue for biomolecular sensing, providing insight into the next-generation of photoelectrochemical biosensing and organic bioelectronics. Herein, this work validates the direct enzymatic biocatalytic precipitation (BCP) modulation on a flower-like Bi2S3 photosensitive gate for high-efficacy OPECT operation with high transconductance (gm), which is exemplified by a prostate-specific antigen (PSA)-dependent hybridization chain reaction (HCR) and subsequent alkaline phosphatase (ALP)-enabled BCP reaction toward PSA aptasensing. It has been shown that light illumination could ideally achieve the maximized gm at zero gate bias, and BCP could efficiently modulate the device's interfacial capacitance and charge-transfer resistance, resulting in a significantly changed channel current (IDS). The as-developed OPECT aptasensor realizes good analysis performance for PSA with a detection limit of 10 fg mL-1. This work features direct BCP modulation of organic transistors and is expected to stimulate further interest in exploring advanced BCP-interfaced bioelectronics with unknown possibilities.

A digital multimeter-based portable photoelectrochemical immunoassay for the detection of cardiac troponin I with enzymatic biocatalytic precipitation.

Early diagnosis of acute myocardial infarction (AMI) can significantly reduce mortality, which can be achieved by the highly sensitive detection of AMI-specific cardiac troponin I (cTnI) biomarkers. Herein a highly sensitive and portable photoelectrochemical (PEC) immunoassay for the detection of cTnI was innovatively fabricated based on an efficient photocurrent response of Cu2O coupling with a split-type enzymatic biocatalytic precipitation reaction with a digital multimeter readout. Initially, Cu2O cubic nanomaterials with a good photocurrent response were obtained by facile green room temperature synthesis and dropped on fluorine-doped tin oxide (FTO) plates as photoactive materials (Cu2O/FTO). In the presence of target cTnI, horseradish peroxidase (HRP) on the detection antibody catalyzes the substrate 4-chloro1-naphthol (4-CN) to produce insoluble precipitates of benzo-4-chlorohexadienone (4-CD) on Cu2O/FTO with the assistance of H2O2, resulting in a decrease in the photocurrent of the Cu2O/FTO electrode. To make the whole inspection process more concise and efficient, we used a flashlight and a digital multimeter as the excitation light source and reading device for the PEC sensing system, respectively. Under the optimal conditions of immunoreaction time, pH, and loading, the photocurrent of Cu2O/FTO decreased with increasing target cTnI concentration with a limit of detection (LOD) of 4.7 pg mL-1 in the operating range of 0.01-10 ng mL-1. It is of interest that the developed portable PEC immunoassay is also capable of detecting cTnI in human serum samples with acceptable accuracy compared to the reference cTnI enzyme-linked immunosorbent assay (ELISA) method while maintaining portability and sensitivity.

Photoelectrochemical immunoassay for thyroglobulin on nanogold-functionalized BiVO4 photoanode coupling with enzymatic biocatalytic precipitation

Methods derived from photoelectrochemical (PEC) have been constructed for immunoassays, but most involve the split-type immunoreaction modes, and thus easily cause unpredictable intermediate precision. Herein, we innovatively designed an integrated PEC immunosensing platform for the quantitative monitoring of thyroglobulin (TG) on the gold nanoparticles (AuNPs)-functionalized BiVO4 photoanode coupling with enzymatic biocatalytic precipitation (EBCP). This sensing system could simultaneously implement the immunoreaction and photocurrent measurement. Anti-TG capture antibodies were modified onto AuNPs-decorated BiVO4 photoelectrode. A sandwich-type immunoreaction was carried out in the presence of target TG using horseradish peroxidase (HRP)-conjugated anti-TG detection antibody. The carried HRP molecules catalyzed 4-chloro-1-naphthol (4-CN) to generate an insoluble benzo-4-chlorohexadienone product on the photoanode in the presence of peroxide hydrogen, thereby decreasing the photocurrent. Under optimal conditions, the PEC immunosensors gave good photocurrent responses toward target TG within the dynamic range of 0.01–10 ng mL−1 at a detection limit of 7.6 pg mL−1. Good repeatability and precision, high specificity and acceptable storage stability were acquired during the measurement. No significant differences were encountered for screening 15 human serum specimens between the developed PEC immunoassay and commercially available enzyme-linked immunosorbent assay (ELISA) method for the detection of target TG. Significantly, PEC immunosensing system offers promise for simple and cost-effective analysis of disease-related biomarkers.

In2O3/CdIn2S4 heterojunction-based photoelectrochemical immunoassay of carcinoembryonic antigen with enzymatic biocatalytic precipitation for signal amplification

This work reported a split-type photoelectrochemical (PEC) immunoassay for the detection of carcinoembryonic antigen (CEA) based on target-induced biocatalytic precipitation (BCP) by using In2O3/CdIn2S4 heterojunctions as the photosensitizers. The synthesized In2O3/CdIn2S4 heterojunctions improved the efficiency of charge separation and shortened the electron convey path to enhance the photocurrent, thus exhibiting high conductivity and low complexation rates of photogenerated electrons and holes. In the presence of CEA, horseradish peroxidase (HRP) catalyzed 4-chloro-1-naphthol (4-CN) to produce benzo-4-chloro-hexadienone (4-CD) through H2O2. Then, 4-CD was deposited onto the surface of In2O3/CdIn2S4 to reduce the photocurrent and realized the signal amplification. The PEC immunoassay revealed an excellent photocurrent toward target CEA within a wide range of 0.01–50 ng mL−1 at a low limit of detection of 2.8 pg mL−1 under the optimum conditions. Multiple switching light excitation tests demonstrated the good reliability and stability of the fabricated PEC biosensor. The accuracy was acceptable in comparison with human CEA enzyme-linked immunosorbent assay (ELISA) kit.

In-situ synthesis of 3D Cu2O@Cu-based MOF nanobelt arrays with improved conductivity for sensitive photoelectrochemical detection of vascular endothelial growth factor 165

Construction of novel photoelectrochemical (PEC) materials with unique structures can effectively improve the photoelectric conversion efficiency. Here, a self-supported Cu2O@Cu-MOF/copper mesh (CM) nanobelt arrays with high specific surface area, high orientation, and high photoelectric conversion performance is obtained by in-situ grown strategy. Such PEC aptasensor is constructed based on the Cu2O@Cu-MOF/CM combined with rolling circle amplification and enzymatic biocatalytic precipitation for vascular endothelial growth factor 165 analysis. This strategy achieves excellent cooperative signal amplification, which greatly improves the detection sensitivity. The PEC aptasensor exhibited a wide calibration ranged from 10 to 1 × 108 fM with a detection limit down to 2.3 fM (S/N = 3). The construction of semiconductor@MOFs has developed the potential application of MOFs in photoelectrochemical and found a reliable path for ultrasensitive detection of biomarkers.

A competitive immunoassay for electrochemical impedimetric determination of chlorpyrifos using a nanogold-modified glassy carbon electrode based on enzymatic biocatalytic precipitation.

A direct competitive impedimetric immunoassay for chlorpyrifos (CPF) was developed that is based on the specific affinity of immunoassay and the enzymatic biocatalytic precipitation amplification strategy. The CPF antibody (anti-CPF) was anchored onto an electro-deposited nanogold modified glassy carbon electrode surface by adsorption of the Au-NH2 bond and Au-SH bond. This improved the electrode reactivity and the loading amount of anti-CPF. Abundant horseradish peroxidase (HRP) and bovine serum albumin-CPF (BSA-CPF) were anchored onto spherical gold nanoparticles (AuNPs, 16 ± 2nm) to form HRP-AuNP-BSA-CPF (analyte competitor). CPF determination was achieved when the competitive immunoassay occurred between CPF and analyte competitor with anti-CPF. In the presence of H2O2 and 4-chloro-1-naphthol, anenzyme-mediated biocatalytic precipitation process was triggered and produced an insoluble 4-chloro-1(4H)-naphthalenone. This insoluble substance increased the Faradaic impedance of the base electrode. The impedimetric signal was determined at the formal potential of 220mV and alternating voltage of 10mV. This signal decreased with increasing concentration of CPF over a linear range of 1.0 × 10-3ngmL-1~10ngmL-1 with a detection limit of 0.070pgmL-1. The immunoassay has been tested for determination of chlorpyrifos in complex matrices such as artificially spiked vegetables with recoveriesin the range 85 to 110%. The relative standard deviations were less than 7.5%. Graphical abstractSchematic representation of electrochemical impedimetric immunoassay for chlorpyrifos determination before enzymatic biocatalytic precipitation (BCP, red line) process and after BCP process (blue line).

In situ amplified QCM immunoassay for carcinoembryonic antigen with colorectal cancer using horseradish peroxidase nanospheres and enzymatic biocatalytic precipitation.

Methods based on enzyme labels or nano labels have been developed for immunoassays, but most of them have low sensitivity and are unsuitable for low-abundance protein diagnostics and biosecurity. Herein, an innovative quartz crystal microbalance (QCM) immunosensing method was designed for high-efficiency detection of carcinoembryonic antigen (CEA) from serum samples with colorectal cancer patients by using horseradish peroxidase (HRP) nanoparticles as the enhancer, accompanying enzymatic biocatalytic precipitation (EBCP) toward 4-chloro-1-naphthol (4-CN) on an anti-CEA capture antibody-conjugated QCM probe. Initially, HRP nanospheres were synthesized on the basis of the reverse micelle method with the assistance of glutaraldehyde cross-linking, and then covalently conjugated onto polyclonal anti-CEA detection antibodies. The QCM immunosensing probe was prepared by immobilizing monoclonal anti-CEA capture antibodies on an l-cysteine-modified gold substrate. In the presence of target CEA, a sandwich-type immunoreaction was carried out between capture antibody and detection antibody, thereby resulting in the attachment of HRP nanospheres on the gold probe. Upon addition of 4-CN in the QCM cell, the carried HRP nanospheres catalyzed the 4-CN oxidation to produce an insoluble precipitate on the gold electrode, thus causing a change in the frequency. Relative to the conventional HRP-labeled strategy and direct antigen-antibody reaction, improved analytical features were obtained with HRP nanospheres. With the HRP nanosphere labeling method, the factors influencing the performance of the immunoassay were also studied. The covalent conjugation of antibodies with HRP nanospheres and the gold substrate achieved a good repeatability and intermediate precision down to 10.7%. Under optimum conditions, the frequency variation of the QCM immunoassay was proportional to the target CEA concentration within a dynamic linear range of 0.01-100 ng mL-1 with a detection limit (LOD) of 7.8 pg mL-1. In addition, the developed QCM immunoassay showed high specificity and long-term storage stability, and could be used for the analysis of human serum samples with consistent results in comparison with those obtained from the commercial enzyme-linked immunosorbent assay (ELISA) method.

Ti3C2 MXene nanosheet-based capacitance immunoassay with tyramine-enzyme repeats to detect prostate-specific antigen on interdigitated micro-comb electrode

An interdigitated capacitance immunosensing system based enzymatic biocatalytic precipitation on micro-comb electrode was designed for the sensitive detection of prostate-specific antigen (PSA) by coupling Ti3C2 MXenes with tyramine signal amplification strategy. The immunosensor was prepared by immobilizing anti-PSA capture antibody on MXenes-coated interdigitated electrode, whereas gold nanoparticles heavily functionalized with horseradish peroxidase (HRP) and detection antibody were utilized as the signal-transducer tags. Introduction of interdigitated electrode was expected to enhance the sensitivity of capacitance immunosensor. This system mainly consisted of the sandwich-type immunoreaction, formation of tyramine-HRP repeats on gold nanoparticle and enzymatic biocatalytic precipitation. The concatenated HRP through the tyramine oxidized numerous 4-chloro-1-naphthol molecules into insoluble benzo-4-chlorohexadienone with the help of H2O2, and coated the modified immunosensor to keep free ions away from the electrode, thus causing the local alteration in the capacitance. Under optimum conditions, the change of the immunosensor in the capacitance increased with the increasing target PSA concentrations from 0.1 ng mL−1 to 50 ng mL−1 at a detection limit of 0.031 ng mL−1. Moreover, the interdigitated capacitance immunosensor showed good reproducibility, high specificity and acceptable accuracy for the analysis of human serum specimens in comparison with those obtained from commercial human PSA ELISA kit. Importantly, Ti3C2 MXenes-based interdigitated capacitance transducer open new opportunities for protein diagnostics and biosecurity.

Enzyme-loaded liposome with biocatalytic precipitation for potentiometric immunoassay of thyroid-stimulating hormone in thyroid carcinoma

A simple and feasible potentiometric immunosensing platform based on enzymatic biocatalytic precipitation technique was designed for the sensitive detection of thyroid-stimulating hormone (TSH; a typical kind of biomarkers for thyroid carcinoma), using horseradish peroxidase (HRP)-loaded liposome for the signal amplification. To construct such an assay system, a sandwich-type immunoreaction was readily carried out on monoclonal anti-TSH capture antibody-coated electrode by using polyclonal anti-TSH secondary antibody-conjugated HRP-loaded liposome. Accompanying the formation of sandwich-type immunocomplex, the carried liposome was lysed through the added Triton X-100 to release the entrapped HRP molecules, which catalyzed the oxidation of 4-chloro-1-naphthol to produce an insoluble and uncharged organic precipitation on the electrode surface, thereby causing the change of the local electrical potential. Two labeling protocols with and without the liposome were investigated for detection of target TSH, improved analytical features were achieved with HRP-entrapped liposome. Under optimal conditions, the potentiometric immunosensor had good responses for TSH detection within the linear range of 0.01–30 μIU/mL at a detection limit of 0.0067 μIU/mL. Good reproducibility, high specificity and long-time stability were acquired during the assay procedure. Importantly, a well-matched accuracy between the potentiometric immunosensor and commercial human TSH ELISA kit was gave for the analysis of human serum samples.

Ultrasensitive photoelectrochemical detection of microcystin-LR based on hybridization chain reaction assisted exciton-plasmon interaction and enzymatic biocatalytic precipitation

A competitive photoelectrochemical (PEC) immunosensor for microcystin-LR (MC-LR) detection was developed based on hybridization chain reaction (HCR), exciton-plasmon interactions (EPI) and enzymatic biocatalytic precipitation (BCP) multiple cascade amplification strategy. Firstly, The CdS/Fe2O3 co-sensitized TiO2 nanorod arrays were directly grown on the FTO electrode to immobilize antigens, while Au@polyaniline nanocomposites were used to immobilize secondary antibody as the recognition of MC-LR antibody and a DNA primer as the initiator. Secondly, by using HCR, the DNA chain was associated with streptavidin-labeled alkaline phosphatase decorated gold nanoparticles, which can induce silver metallization on the gold nanoparticles and insoluble biocatalytic precipitation, thus the photocurrent can be changed by energy transfer and the inhibition of electron conduction. Taking the advantage of multiple amplification strategy, the immunosensor showed a linear range from 0.5 ng/L to 100 μg/L with a detection limit of 0.3 ng/L. Moreover, it possessed satisfactory performance of stability, selectivity and reproducibility, thus this PEC immunosensor might be attractive in the field of environmental detection.

Highly sensitive electrochemiluminescent immunoassay for neuron-specific enolase amplified by single-walled carbon nanohorns and enzymatic biocatalytic precipitation

A novel amplified electrochemiluminescence (ECL) immunoassay based on single-walled carbon nanohorns (SWCNHs) labels and enzymatic biocatalytic precipitation (BCP) was proposed for the detection of neuron-specific enolase (NSE) for the first time. In this system, the dimercaptosuccinic acid stabilized CdTe (DMSA-CdTe) quantum dots (QDs) as ECL emitter showed excellent ECL behavior and then employed as the NSE antibody (Ab1) immobilization film for the subsequent sandwich-type Ab1-Ag affinity interactions. Improved sensitivity was achieved through using the SWCNHs effectively to expand the amount of secondary antibody (Ab2) and horseradish peroxidase (HRP) loading. In addition to the much enhanced steric hindrance, compared with the single HRP-Ab2, the presence of plentiful HRP would further stimulate the BCP onto the electrode surface for signal amplification, concomitant to the BCP products absorption that lowered ECL intensity. As a result of the multisignal amplification in this ECL immunosensor, it possessed excellent analytical performance. The target NSE could be detected from 1 × 10−9 g L−1 to 1 × 10−3 g L−1 with a detection limit of 4.4 × 10−10 g L−1.

A novel potentiometric immunoassay for carcinoma antigen 15-3 by coupling enzymatic biocatalytic precipitation with a nanogold labelling strategy.

Methods based on potentiometric measurement have been developed for immunoassays, but most exhibit low sensitivities and are unsuitable for early diagnosis of disease. Herein we design a new potentiometric immunosensing platform for the sensitive detection of carcinoma antigen 15-3 (CA 15-3) by coupling with enzymatic biocatalytic precipitation and a nanogold labeling technique. The sandwich-type immunoreaction is carried out on a monoclonal anti-CA 15-3 capture antibody-modified working electrode, using horseradish peroxidase (HRP) and polyclonal anti-CA 15-3 detection antibody-labeled gold nanoparticles. Upon the introduction of target CA 15-3, the carried HRP molecules with an immunocomplex catalyze the oxidation of 4-chloro-1-naphthol (4-CN) into the insoluble benzo-4-chlorohexadienone. The formed product coated on the surface of the modified electrode results in a change of the electrical potential. Under optimal conditions, the shift in the electrical potential relative to the background signal increases with the increasing target CA 15-3 concentration, and exhibits a good linear relationship within the dynamic range of 0.01-30 U mL-1 at a detection limit of 7.8 mU mL-1. Good precision and reproducibility, and high specificity were acquired for the analysis of 15 human serum specimens, giving well matched results with those obtained from a human CA 15-3 ELISA kit.

WS2 nanosheets-sensitized CdS quantum dots heterostructure for photoelectrochemical immunoassay of alpha-fetoprotein coupled with enzyme-mediated biocatalytic precipitation.

Based on enzymatic biocatalytic precipitation to quench the amplified photocurrent response generated from WS2 nanosheets-sensitized CdS quantum dots heterostructure, a novel photoelectrochemical immunosensor was constructed for sensitive alpha-fetoprotein (AFP) monitoring. The immunosensor comprised an anti-AFP antibody and a horseradish peroxidase-tagged anti-AFP antibody (HRP-Ab2), which served as a capture unit and a signal indicator, respectively. In the presence of AFP, HRP-Ab2 was immobilized on the electrode surface for establishing a sandwich-type immunocomplex via antigen-antibody interaction, and subsequently catalyzed 4-chloro-1-naphthol to form the nonconductive and insoluble precipitate. This precipitation effectively impeded the diffusion and electron transfer of the electron donor, thus achieving decreased photocurrent. Under optimized conditions, excellent linearity range (1 pg mL-1-20 ng mL-1), satisfactory detection limit (0.43 pg mL-1), desirable selectivity and good stability were obtained for the as-designed immunosensor. Moreover, the application of AFP determination in human serum allowed the immunosensor to hold great potential for early diagnostics of some cancer diseases.

Bio-bar-code-based photoelectrochemical immunoassay for sensitive detection of prostate-specific antigen using rolling circle amplification and enzymatic biocatalytic precipitation

Methods based on photoelectrochemistry have been developed for immunoassay, but most involve in a low sensitivity and a relatively narrow detectable range. Herein a new bio-bar-code-based split-type photoelectrochemical (PEC) immunoassay was designed for sensitive detection of prostate-specific antigen (PSA), coupling rolling circle amplification (RCA) with enzymatic biocatalytic precipitation. The bio-bar-code-based immunoreaction was carried out on monoclonal anti-PSA antibody (mAb1)-coated microplate using primer DNA and polyclonal anti-PSA antibody-conjugated gold nanoparticle (pDNA-AuNP-pAb2) with a sandwich-type assay format. Accompanying the immunocomplex, the labeled primer DNA on gold nanoparticle readily triggered RCA reaction in the presence of padlock probe/dNTPs/ligase/polymerase. The RCA product with a long single-stranded DNA could cause the formation of numerous hemin/G-quadruplex-based DNAzyme concatamers. With the assistance of nicking endonuclease, DNAzyme concatamers were dissociated from gold nanoparticle, which catalyzed the precipitation of 4-chloro-1-naphthol in the presence of H2O2 onto CdS nanorods-coated electrode (as the photoanode for the generated holes). The formed insoluble precipitate inhibited the electron transfer from the solution to CdS nanorods-modified electrode by using ascorbic acid as the electron donor. Under the optimum conditions, the photocurrent of the modified electrode decreased with the increasing of PSA concentration. A detectable concentration for target PSA with this system could be achieved as low as 1.8pgmL−1. In addition, our strategy also showed good reproducibility, high specificity and accuracy matched well with commercial PSA ELISA kits for real sample analysis. These remarkable properties revealed that the developed PEC immunoassay has great potential as a useful tool for the detection of PSA in practical application.

CdS:Mn quantum dot-functionalized g-C3N4 nanohybrids as signal-generation tags for photoelectrochemical immunoassay of prostate specific antigen coupling DNAzyme concatamer with enzymatic biocatalytic precipitation

A new photoelectrochemical (PEC) immunosensor based on Mn-doped CdS quantum dots (CdS:Mn QDs) on g-C3N4 nanosheets was developed for the sensitive detection of prostate specific antibody (PSA) in biological fluids. The signal derived from the as-synthesized Cd:Mn QDs-functionalized g-C3N4 nanohybrids via a hydrothermal method and was amplified through DNAzyme concatamers on gold nanoparticles accompanying enzymatic biocatalytic precipitation. Experimental results by UV–vis absorption spectra and photoluminescence revealed that CdS:Mn QDs/g-C3N4 nanohybrids exhibited higher photocurrent than those of CdS:Mn QDs and g-C3N4 alone. Upon addition of target PSA, a sandwich-type immunoreaction was carried out between capture antibodies and the labeled detection antibodies. Accompanying introduction of gold nanoparticles, the labeled initiator strands on the AuNPs triggered hybridization chain reaction and the formation of DNAzyme concatamers in the presence of hemin. The formed DNAzyme catalyzed 4-chloro-1-naphthol (4-CN) to produce an insoluble/insulating precipitate on the Mn:CdS QDs/g-C3N4, and blocked the light harvesting of Mn:CdS QDs/g-C3N4, thus resulting in the decreasing photocurrent. Under optimal conditions, the immunosensor exhibited good photocurrent responses for determination of target PSA, and allowed detection of PSA at a concentration as low as 3.8pgmL−1. The specificity, reproducibility and precision of this system were acceptable. Significantly, this methodology was further evaluated for analyzing human serum samples, giving well-matched results with referenced PSA enzyme-linked immunosorbent assay (ELISA) method.

Sandwich-like electrochemiluminescence aptasensor based on dual quenching effect from hemin-graphene nanosheet and enzymatic biocatalytic precipitation for sensitive detection of carcinoembryonic antigen

A new and simple sandwich-like electrochemiluminescence (ECL) aptasensor for carcinoembryonic antigen (CEA) assay was fabricated based on the dual quenching effect from hemin-graphene (H-rGO) nanosheet and enzymatic biocatalytic precipitation (BCP) on the Au-CdS nanocomposites-based ECL system. In this aptasensor platform, flower-like spherical Au-CdS nanocomposites were used as ECL luminophores and exhibit a strong ECL signal. The rGO nanosheet was used as a supporter to immobilize hemin molecules via π-π stacking interactions. Due to the steric hindrance and quenching effect of rGO, the ECL intensity decreased by the construction of the sandwich “CEA aptamer I (NH2-DNA)-CEA-aptamer II” (H-rGO-aptamer II) mode. In the process of BCP, the ECL intensity further decreased because the hemin with intrinsic peroxidase-like catalytic activity could oxidize the 4-chloro-1-naphthol (4-CN) to produce an insoluble precipitation on the sensor. Using this dual quenching strategy, the prepared aptasensor exhibits a linear range from 0.8pg/mL to 4ng/mL and a detection limit of 0.28pg/mL. This ECL aptasensor has simple design and undemanding in operation and was utilized to determine the content of CEA in complex samples with recoveries of 95.0% to 115.8%. Moreover, no any chemical modification of aptamer was required, suggesting that the proposed ECL aptasensor could be applied for the detection of diverse proteins just by altering the aptamer sequence.

One-step hydrothermal treatment to fabricate Bi2WO6-reduced graphene oxide nanocomposites for enhanced visible light photoelectrochemical performance.

Considering that ultraviolet light may cause the denaturation of biomaterials, searching for and engineering innovative and advanced nanomaterials with excellent photoelectrochemical properties under visible light illumination are of great significance in the fundamental understanding and application of photoelectrochemical (PEC) sensors. As a widely applied visible light response material, the applications of Bi2WO6 in PEC fields were restricted because of the rapid recombination of photoinduced electron-hole pairs. In this work, Bi2WO6 functionalized reduced oxide (Bi2WO6-rGO) nanocomposites (NCs) were prepared by a one-step solvothermal method. After optimizing the content of rGO, the Bi2WO6-rGO2.94% NCs displayed enhanced photocurrent intensity (the starting mass ratios of GO to Bi2WO6 = 0.0294), which was nearly 2.7-fold compared to that of pure Bi2WO6 nanoparticles because of the separation of the photoinduced carriers and the enhancement of visible light absorption. Based on the coupling of Pb2+-induced allosteric transition of G-quadruplex DNAzyme and the enzymatic biocatalytic precipitation (BCP), Bi2WO6-rGO2.94% NCs were applied in the construction of a novel PEC sensor for the determination of Pb2+. The as-fabricated PEC sensor exhibited good anti-interference ability and a good linear relationship was obtained between the photocurrent intensity and the logarithm of the Pb2+ concentration over a concentration range from 0.01 to 50 μM and with a detection limit of 3.3 nM (S/N = 3), indicating that Bi2WO6-rGO NCs would be promising materials for PEC sensing.

Nanogold-functionalized g-C3N4 nanohybrids for sensitive impedimetric immunoassay of prostate-specific antigen using enzymatic biocatalytic precipitation

This work reports on a new impedimetric immunosensing strategy for sensitive detection of prostate-specific antigen (PSA) in biological fluids. The assay was carried out on monoclonal anti-PSA capture antibody-modified glassy carbon electrode with a sandwich-type detection format. Gold nanoparticles-decorated g-C3N4 nanosheets (AuNP/g-C3N4), synthesized by the wet-chemistry method, were utilized for the labeling of polyclonal anti-PSA detection antibody and horseradish peroxidase (HRP). Upon target PSA introduction, the sandwiched immunocomplex could be formed between capture antibody and detection antibody. Followed by the AuNP/g-C3N4, the labeled HRP could catalyze 4-choloro-1-naphthol into benzo-4-chlorohexadienone. The as-generated insoluble product was coated on the electrode surface, thus increasing the Faradaic impedance of Fe(CN)64−/3− indicator between the solution and the base electrode. Under the optimal conditions, the impedance increased with the increasing target PSA in the sample, and exhibited a wide linear range from 10pgmL−1 and 30ngmL−1 with a detection limit of 5.2pgmL−1. A repeatability and intermediate precision of <14% was accomplished. The specificity and method accuracy in comparison with commercial PSA ELISA kit for analysis of human serum specimens were relatively satisfactory.