Labels For Signal Amplification Research Articles

Expression of Concern: Advances in layered double hydroxide based labels for signal amplification in ultrasensitive electrochemical and optical affinity biosensors of glucose

Expression of Concern: Advances in layered double hydroxide based labels for signal amplification in ultrasensitive electrochemical and optical affinity biosensors of glucose

An Electrochemical Immunosensor for Sensitive Detection of Cardiac Troponin I Based on the Amplification Effect of Asymmetric Bowl-Shaped Mesoporous Nanospheres

Here, a sandwich-type electrochemical immunosensor was constructed to detect cardiac troponin I (cTnI) via asymmetric bowl-shaped PdAgFe mesoporous nanospheres (PdAgFe ABMS) as signal amplification label and core–shell cubic Au/Co-LDH@ZIF-67 as substrate material. PdAgFe ABMS prepared by dual-template directional anisotropic island growth method has abundant mesoporous channels to accelerate molecular mass transfer in solution. In particular, the asymmetric bowl-like structure allows more active sites to be exposed, which improves the utilization of atoms to stabilize and high current response signals. The synergistic effect between PdAgFe increased the activation energy of the catalytic reaction and further amplified the current signal. In addition, the biosensing interface based on Au/Co-LDH@ZIF-67 not only exhibits a high electron transfer rate, but also can capture more bioactive molecules. Under the optimal conditions, the constructed immunosensor was detected to exhibit a low limit of detection (LOD, 4.47 fg ml−1) and a wide detection range (10 fg ml−1–100 ng ml−1). This work provides an accurate and convenient scheme for the clinical detection of cTnI.

Dual-signaling electrochemical immunosensor for ultra-sensitive detection of procalcitonin based on the hydrogen evolution and photoelectric signals of AuPt/BP

In recent years, noble metal catalysts have been extensively studied in terms of hydrogen evolution reaction (HER), but there has been less research on the construction of immunosensor based on the catalytic signal amplification strategy of noble metal. Based on the excellent HER and photoelectric performance of AuPt nanoslices modified black phosphorus nanoflakes (AuPt/BP) in neutral medium, we reported a dual-signal electrochemical immunosensor, which uses AuPt/BP as signal amplification label for the detection of procalcitonin (PCT). Due to the charge transfer between AuPt and BP, AuPt/BP has better HER activity and photoelectric performance than single AuPt or BP, which realized the construction of dual-signal electrochemical immunosensors and the improvement of detection sensitivity. In addition, the presence of BP makes AuPt/BP has better dispersion and larger surface area, which can load more secondary antibody (Ab2) and realize the signal amplification of the immunosensor. The linear ranges of PCT detection based on HER and photoelectric signals are 1.96 fg mL−1 ∼ 0.196 ng mL−1 and 1.96 fg mL−1 ∼ 19.6 pg mL−1, and the detection limits of PCT with HER and photoelectric signals are 0.88 fg mL−1 and 0.99 fg mL−1.

Digital and Absolute Assays for Low Abundance Molecular Biomarkers.

There has been a recent surge of advances in biomolecular assays based on the measurement of discrete molecular targets as opposed to signals averaged across molecular ensembles. Many of these "digital" assay designs derive from now-mature technologies involving single-molecule imaging and microfluidics and provide an assortment of new modalities to quantify nucleic acids and proteins in biospecimens such as blood and tissue homogenates. A primary new benefit is the robust detection of trace analytes at attomolar to femtomolar concentrations for which many ensemble assays cannot distinguish signals above noise levels. In addition, multiple biomolecules can be differentiated within a mixture using optical barcodes, with much faster and simpler readouts compared with sequencing methods. In ideal digital assays, signals should, in theory, further represent absolute molecular counts, rather than relative levels, eliminating the need for calibration standards that are the mainstay of typical assays. Several digital assay platforms have now been commercialized but challenges hinder the adoption and diversification of these new formats, as there are broad needs to balance sensitivity and dynamic range of detection, increase analyte multiplexing, improve sample throughput, and reduce cost. Our lab and others have developed technologies to address these challenges by redesigning molecular probes and labels, improving molecular transport within detection focal volumes, and applying solution-based readout methods in flow.This Account describes the principles, formats, and design constraints of digital biomolecular assays that apply optical labels toward the goal of simple and routine target counting that may ultimately approach absolute readout standards. The primary challenges can be understood from fundamental concepts in thermodynamics and kinetics of association reactions, mass transport, and discrete statistics. Major advances include (1) new inorganic nanocrystal probes for more robust counting compared with dyes, (2) diverse molecular amplification tools that endow attachment of numerous labels to single targets, (3) specialized surfaces with patterned features for electromagnetic coupling to labels for signal amplification, (4) surface capture enhancement methods to concentrate targets through disruption of diffusion depletion zones, and (5) flow counting in which analytes are rapidly counted in solution without pull-down to a surface. Further progress and integration of these tools for biomolecular counting could improve the precision of laboratory measurements in life sciences research and benefit clinical diagnostic assays for low abundance biomarkers in limiting biospecimen volumes that are out of reach of traditional ensemble-level bioassays.

Photoelectrochemical Immunosensor Based on a 1D Fe2O3/3D Cd-ZnIn2.2Sy Heterostructure as a Sensing Platform for Ultrasensitive Detection of Neuron-Specific Enolase.

Lung cancer is a high-mortality cancer related to the concentration of neuron-specific enolase (NSE). In this work, a sandwich-type photoelectrochemical (PEC) immunosensor was constructed for ultrasensitive detection of NSE, which is based on iron trioxide/indium zinc cadmium sulfide (Fe2O3/Cd-ZnIn2.2Sy) as a sensing platform and Ag-modified polyaniline (Ag@PANI) as a signal amplification label. The 1D Fe2O3 porous nanorods with a large specific surface area were synthesized by calcination of Fe-MIL-88A and etching of NaOH. To improve the photocurrent response, the 3D architecture Cd-ZnIn2.2Sy was combined with the 1D Fe2O3 porous nanorods to form a 1D Fe2O3/3D Cd-ZnIn2.2Sy heterostructure. Specifically, the Fe2O3/Cd-ZnIn2.2Sy heterostructure with a good energy level matching (the two can form a stepped energy level matching, which accelerates the transfer rate of electrons) can improve the separation efficiency of electron-hole pairs (e-/h+) under visible light irradiation, which enhances the photocurrent response. Ag@PANI has a strong electron transport capability and can be used as a secondary antibody marker for the signal amplification of the immunosensor. The sensor exhibits a good linear detection range of 100 fg/mL to 100 ng/mL with a low detection limit of 33.5 fg/mL. Moreover, the constructed sandwich-type PEC immunosensor shows good performance and possesses excellent specificity, selectivity, and stability over a period of 4 weeks for NSE detection. With these excellent properties, the immunosensor can be extended to analyze and diagnose other disease biomarkers.

Advances in layered double hydroxide based labels for signal amplification in ultrasensitive electrochemical and optical affinity biosensors of glucose

Since the development of enzyme electrodes, the research area of glucose biosensing has seen outstanding progress and improvement. Numerous sensing platforms have been developed based on different immobilization techniques and improved electron transfer between the enzyme and electrode. Interestingly, these platforms have consistently used innovative nanostructures and nanocomposites. In recent years, layered double hydroxides (LDHs) have become key tools in the field of analytical chemistry owing to their outstanding features and benefits, such as facile synthesis, cost-effectiveness, substantial surface area, excellent catalytic performance, and biocompatibility. LDHs are often synthesized as nanomaterial composites or manufactured with specific three-dimensional structures. The purpose of this review is to illustrate the biosensing prospects of LDH-based glucose sensors and the need for improvement. First, various clinical and conventional approaches for glucose determination are discussed. The definitions, types, and various synthetic methodologies of LDHs are then explained. Subsequently, we discuss the various research studies regarding LDH-based electrochemical and optical assays, focusing on modified systems, improved electron transfers pathways (through developments in surface science), and different sensing designs based on nanomaterials. Finally, a summary of the current limitations and future challenges in glucose analysis is described, which may facilitate further development and applications.

An ultrasensitive electrochemical aptasensor for microcystin-LR detection using core-satellite gold nanoparticle/silver nanocluster nanoassemblies as labels for signal amplification

In this work, an ultrasensitive electrochemical aptasensor for microcystin-LR (MC-LR) detection had been developed using core-satellite gold nanopaticle/silver nanocluster nanoassemblies (sDNA-AuNP@AgNC) as electrochemical labels. sDNA-AuNP@AgNC was characterized by transmission electron microscopy, and X-ray diffraction and ultraviolet-visible absorption spectroscopies. Functional cytosine-rich single-stranded DNA (sDNA) integrating both template sequence and recognition sequence for hybridization was immobilized on AuNP surface through Au-S bond to prepare AuNP conjugations (sDNA-AuNP). After hybridization of sDNA-AuNP and incubation of AgNO3 solution, generous Ag+ ions were encapsulated into sDNA-AuNP at electrode by the strong C-Ag+-C structure. AgNC was in situ synthesized on sDNA-AuNP to form core-satellite sDNA-AuNP@AgNC nanoassemblies, which showed enhanced electrocatalytic performance toward H2O2 reduction and produced a detection signal on aptasensor surface. In the presence of MC-LR, MC-LR aptamer preferentially bound to MC-LR, and the electrochemical signal decreased. A competitive aptasensing assay was used in our work, and the efficient signal amplification of sDNA-AuNP@AgNC made the MC-LR aptasensor have a low detection limit of 0.06 pM (S/N = 3) and a wide linear range from 0.2 pM to 200 nM. This designed aptasensor showed excellent selectivity, reproducibility and stability, and had been applied to detect MC-LR concentration in real samples.

Ag2S quantum dots loaded dendritic mesoporous silica nanospheres as signal amplification labels for ultrasensitive electrochemical immuno-biosensor for Staphylococcus aureus

An electrochemical immuno-biosensor based on Ag 2 S/DMSNs labels was established to detect S. aureus . • An electrochemical immuno-biosensor based on Ag 2 S/DMSNs labels was established to detect S. aureus . • Using DMSNs for Ag 2 S QDs enrichment and signal amplification to improve the detection sensitivity. • A wide linear detection range from 10 to 10 8 CFU mL −1 , with a detection limit of 2 CFU mL −1 . • The immuno-biosensor showed excellent selectivity and stability. • The immuno-biosensor was successfully applied to detect actual samples. Developing novel signal amplification labels in electrochemical immuno-biosensors for ultrasensitive, fast and selective detection of foodborne pathogen is urgent and significant for people's health and life safety. Herein, dendritic mesoporous silica nanospheres (DMSNs) loaded with silver sulfide quantum dots (Ag 2 S QDs) were fabricated and employed as signal amplification labels for highly sensitive electrochemical detection of Staphylococcus aureus ( S. aureus ). DMSNs were treated with 3-aminopropyltrioxysilane to introduce amino group on surfaces to facilitate the immobilization of Ag 2 S QDs. Benefiting from the highly accessible surface areas and large pore channels characteristics given by the unique radial flower-like structure of DMSNs, large amount of Ag 2 S QDs were loaded into the surfaces and pores of the DMSNs to form Ag 2 S/DMSNs. To specifically recognize S. aureus cells, Ag 2 S/DMSNs were modified by anti- S. aureus antibody (Ab) to form Ab-Ag 2 S/DMSNs. When the sandwich-type electrochemical immuno-biosensor operated, Ag(Ⅰ) ions were released from the Ag 2 S/DMSNs label by HNO 3 leaching, and the detection of S. aureus was realized by the differential pulse voltammetry. The electrochemical signal of the prepared immuno-biosensor was substantially magnified when compared to the immuno-biosensor employing Ag 2 S QDs as signal label, since much more Ag 2 S QDs were labeled to each bacterial cell due to the high loading of Ag 2 S QDs on the DMSNs. As a consequence, the developed immuno-biosensor was capable of detecting S. aureus cells down to a limit of 2 colony forming units per mL (CFU mL −1 ) and exhibited a wide linear detection range from 10 CFU mL −1 to 10 8 CFU mL −1 . In addition, the immuno-biosensor showed excellent selectivity and stability for the detection of S. aureus , and was successfully applied to detected S. aureus in milk samples.

Electrochemical “signal on/off” paper-based aptasensor for ochratoxin A detection based on MXene-Au and Pt@NiCo-LDH-catalyzed signal amplification

Electrochemical sensing technology integrated with a paper-based analytical device (PAD) offers an effective method for analyte detection. Nevertheless, it is still challenging to realize reliable and sensitive analysis owing to the basic shortcomings (inferior conductivity and high batch-to-batch variability) of paper-based working electrodes (WE) and lack of efficient signal amplification label. Herein, we proposed a novel electrochemical aptasensor to detect ochratoxin A (OTA), with MXene-Au as sensing substrates and Pt nanoparticles (NPs) anchored hollow structure NiCo-layered double hydroxides (Pt@NiCo-LDH) as signal amplification materials. The complementary DNA (cDNA) was firstly assembled onto the MXene-Au/WE via Au-S bonds. Then aptamer (apta)-binding Pt@NiCo-LDH with excellent peroxidase (POD)-like activity was immobilized through hybridization to trigger the “signal on” state, generating a significant electrochemical signal. The presence of OTA enabled the dissociation of the apta-cDNA hybrid, releasing signal amplification labels to achieve “signal off” state. Based on the “signal on/off” strategy, the aptasensor exhibited a wider linear range from 20 fg/mL to 100 ng/mL and a lower limit of detection of 8.9 fg/mL (S/N = 3). This work provided a new avenue for the versatile design of electrochemical paper-based platform that enabled the on-site detection of various analytes.

Study on the self-assembly and signal amplification ability of nucleic acid nanostructure with the nanopipette

Nanopipette as a member of solid-state nanopores has been developed to detect a set of biological molecules. Although the size of the nanopipette can be adjusted artificially, the direct detection of small molecules is still challenging, which is limited by the precision of the nanopipette preparation. In this work, the translocation characteristics of DNA tetrahedrons with varying degrees of the assembly were studied to evaluate their self-assembly process and the advantage of tetrahedral DNA nanostructures as a signal amplification label for biomarkers detection based on current blockages. Self-assembly of different number of single-stranded DNA causes the DNA nanostructure in different shapes. Through the complete assembly of DNA tetrahedron, we demonstrate that the nanopore signal-to-noise ratio is significantly increased and the event signal becomes more stable and significant. Therefore, these attributes allow us to gain more insight into the assembly process of DNA nanostructures and we can use tetrahedral DNA nanostructure to develop an effective assay for identifying small molecules with the nanopipette.

A highly sensitive bio-barcode immunoassay for multi-residue detection of organophosphate pesticides based on fluorescence anti-quenching

Balancing the risks and benefits of organophosphate pesticides (OPs) on human and environmental health relies partly on their accurate measurement. A highly sensitive fluorescence anti-quenching multi-residue bio-barcode immunoassay was developed to detect OPs (triazophos, parathion, and chlorpyrifos) in apples, turnips, cabbages, and rice. Gold nanoparticles were functionalized with monoclonal antibodies against the tested OPs. DNA oligonucleotides were complementarily hybridized with an RNA fluorescent label for signal amplification. The detection signals were generated by DNA-RNA hybridization and ribonuclease H dissociation of the fluorophore. The resulting fluorescence signal enables multiplexed quantification of triazophos, parathion, and chlorpyrifos residues over the concentration range of 0.01–25, 0.01–50, and 0.1–50 ng/mL with limits of detection of 0.014, 0.011, and 0.126 ng/mL, respectively. The mean recovery ranged between 80.3% and 110.8% with relative standard deviations of 7.3%–17.6%, which correlate well with results obtained by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The proposed bio-barcode immunoassay is stable, reproducible and reliable, and is able to detect low residual levels of multi-residue OPs in agricultural products.

Highly Sensitive Voltammetric Immunosensing of Cancer Biomarkers HER2 and CA125 Using Gold Nanoparticles Anchored Reduced Graphene Oxide Enzyme-Free Nanolabel

Sandwich type voltammetric immunosensors were developed for the quantitative determination of cancer biomarkers, HER2 (human epidermal growth factor receptor 2), and CA125 (cancer antigen 125). Specific antibodies were immobilized on the gold electrodes by using a self-assembled monolayer of mercaptoundecanoic acid (MUA) activated by EDC-NHS ((1-ethyl-3-(3-dimethylamino propyl) carbodiimide and N-hydroxysuccinimide). Antibody conjugated gold nanoparticles decorated reduced graphene oxide (anti-HER2-Au/rGO and anti-CA125-Au/rGO) were used as enzyme-free nano labels for signal amplification. The sensors were characterized thoroughly by spectroscopic, microscopic, and electrochemical methods. Differential pulse voltammetric (DPV) studies in the presence of thionine revealed that the current signal produced is directly related to the biomarker concentration. A linear range of 0.2 pg ml−1 to 100 ng ml−1 was obtained, which indicated the immunosensors to be highly sensitive in lower concentrations of cancer biomarkers. Finally, the fabricated immunosensors were tested with serum samples spiked with HER2 and CA125. The results obtained from the test confirmed the data collected from clinical labs.

Ultrasensitive Competitive Lateral Flow Immunoassay with Visual Semiquantitative Inspection and Flexible Quantification Capabilities

Antibiotics abuse has caused various problems threatening human health and ecological environment. Monitoring antibiotics residual levels is of great significance, yet still challenging for quantitative point-of-need testing with high-sensitivity and visual capability. Here we developed a competitive lateral flow immunoassay (CLFIA) platform with flexible readout for enrofloxacin (ENR), a regularly added antibiotic. To overcome the limitation of low sensitivity of traditional colloidal gold-based CLFIA, the three-dimensionally assembled gold nanoparticles (AuNPs) within dendritic silica scaffold were fabricated as signal reporters. The assembly structure effectively retained the intrinsic absorption features of hydrophobic AuNPs and greatly enhanced the light extinction ability of a single label for signal amplification. The obtained CLFIA strips can not only achieve qualitative screening of ENR at a very low concentration by naked eye (cutoff value: 0.125 ng/mL), but also enable ultrasensitive quantification of ENR by an optical scanner (limit of detection: 0.00195 ng/mL) or a smartphone (limit of detection: 0.0078 ng/mL). Moreover, to elaborate the visual inspection degree of CLFIA against traditional yes/no interpretation, a novel multirange gradient CLFIA strip was prepared for visually semiquantitative identification of ENR with four concentration ranges. The novel CLFIA platform demonstrated sensitive, specific, and reliable determination of ENR with flexible signal readout and provides a potential and invigorating pathway to point-of-need immunoassay of antibiotics.

Improved ELISA for linoleate-derived diols in human plasma utilizing a polyHRP-based secondary tracer.

Dihydroxyoctadecenoic acids (DiHOMEs) are cytochrome P450 pathway-derived metabolites of linoleic acid, a highly abundant dietary fatty acid. They serve thermogenic functions at low concentrations but, at high concentrations, are involved in proinflammatory and deleterious outcomes in a wide range of pathologies. Hence, the development of a reliable analytical method is critical to elucidate their potential as biomarkers of health, and enzyme-linked immunoassay (ELISA)-based approaches offer unique benefits as alternatives to traditional liquid chromatography-tandem mass spectrometry (LC-MS/MS) systems. Accordingly, an earlier ELISA for DiHOMEs was dramatically improved employing new secondary tracers and geared towards use in human plasma, a universal matrix in biomedical applications, as well as urine. Three ELISA formats, two utilizing polyHRP-based secondary labels for signal amplification, were compared. The best format involved a biotinylated detection antibody and a polyHRP-conjugated streptavidin tracer. Assay detectability was enhanced 20-fold, relative to the original immunoassay, and performance assessments validated precision, selectivity, and robustness. Fast and easy extraction-clean up steps yielded high analytical recovery and permitted the assay to operate in moderate concentrations (up to 20%) of plasma, expanding its practical relevance. Finally, the ELISA was applied towards detection of DiHOMEs in clinical samples and authenticated with complementary LC-MS/MS analysis. Hence, the method provides a valuable analytical tool to investigate the diverse and extensive roles of DiHOMEs in regulatory biology.

Ultrasensitive Double-Channel Microfluidic Biosensor-Based Cathodic Photo-electrochemical Analysis via Signal Amplification of SOD-Au@PANI for Cardiac Troponin I Detection.

Interesting double-channel microfluidic chip integration with a sandwich-type cathodic photo-electrochemical (PEC) biosensor is utilized for ultrasensitive and efficient detection of cardiac troponin I (cTnI) based on a signal amplification strategy. The Pd nanoparticles loading on the I-doped bismuth oxybromide with oxygen vacancies (Pd/I:BiOBr-OVs) as a sensing platform can effectively enhance cathodic photocurrent response by improving the visible light absorption ability with I doping, facilitating the efficiency separation of photogenerated electron-hole pairs with OVs, and increasing the electron-transfer rate with Pd loading, where the photogenerated electron could be captured by dissolved O2 to boost generation of a superoxide anion radical (•O2-). To further enhance the PEC response, a novel superoxide dismutase loaded on gold@polyaniline (SOD-Au@PANI) as a signal amplification label is developed for incubating the detection antibody (dAb). It is particularly noteworthy that SOD can effectively catalyze dismutation of the •O2- to produce H2O2 and O2, and Au@PANI with a good reduction and catalytic property can catalyze the produced H2O2 into H2O and O2. Then, the produced O2 that has been dissolved or adsorbed can capture more photogenerated electrons, resulting in more electron-hole pairs to separate, so as to the cathodic photocurrent signal of this system which can be amplified more significantly. Therefore, a signal amplification cathodic PEC biosensor is prepared for sensitively detecting cTnI, in which a good linearity ranging from 0.1 pg/mL to 100 ng/mL with a low detection limit of 0.042 pg/mL is obtained. Furthermore, the proposed biosensor exhibits excellent sensitivity and high selectivity, which could be extended to detect other disease markers in biological analysis and early disease diagnosis.

A novel sandwich-type electrochemical biosensor enabling sensitive detection of circulating tumor DNA

It is of great importance to accurately analyze circulating tumor DNA (ctDNA), for the reason that it serves as one of the particularly informative cancer biomarkers for disease diagnosis, therapy, and prognosis. However, sensitive detection of ctDNA remains a challenging task and the design of feasible sensing method plays a significant role in ctDNA analysis. In this work, a novel sandwich-type electrochemical biosensor was developed through a facile way for sensitive detection of ctDNA using nanocomposites (MWCNTs-PDA-Au-Pt) as signal probes’ (SPs) label (SPs-label) for signal amplification. The current response of the nanocomposites towards H2O2 reduction was used to quantitatively detect target DNA and distinguish base-mismatched DNA sequences. Characterizations reveal that Au-Pt alloy nanoparticles are uniformly dispersed on MWCNTs-PDA and the resultant MWCNTs-PDA-Au-Pt shows excellent response toward the reduction of H2O2, which could largely amplify the current response. Electrochemical analysis of electrode modification process confirms that the sandwich-type structure was successfully formed through step-wise reactions, including fixation of capture probes (CPs) on the surface of the screen-printed gold electrode, recognition between CPs and target DNA (T-DNA), hybridization between T-DNA and SPs. Under optimal experimental conditions, the proposed ctDNA biosensor exhibits a wide linear range from 1 × 10−15 to 1 × 10−8 mol/L with a detection limit as low as 5 × 10−16 mol/L (S/N = 3), unprecedented selectivity towards T-DNA and other base-mismatched DNAs (even for only single base-mismatched sequences), and superb long-term stability. This work demonstrates the sandwich-type scheme is a promising method for practical applications in clinical ctDNA diagnosis.

Multi-function PtCo nanozymes/CdS nanocrystals@graphene oxide luminophores and K2S2O8/H2O2 coreactants-based dual amplified electrochemiluminescence immunosensor for ultrasensitive detection of anti-myeloperoxidase antibody

BackgroundAnti-myeloperoxidase antibody (anti-MPO) is an important biomarker for anti-neutrophil cytoplasm antibody (ANCA)-associated vasculitides (AAVs). However, the complicated operation procedures and insufficient sensitivity of conventional anti-MPO detection methods limit their application in monitoring efficacy of AAVs in clinical diagnosis. Herein, a dual amplified electrochemiluminescence (ECL) immunosensor based on multi-function PtCo nanozymes/CdS nanocrystals@graphene oxide (PtCo/CdS@GO) luminophores and K2S2O8/H2O2 coreactants has been fabricated for ultrasensitive detection of anti-MPO.ResultsPtCo/CdS@GO luminophores as novel signal amplification labels and nanocarriers to load rabbit anti-mouse IgG were synthesized by co-doping with Pt and Co nanozymes simultaneously with several considerable advantages, including astonishing peroxidase-like catalytic activity, high-efficiency luminescence performance and superior stability in aqueous solutions. Meanwhile, upon the K2S2O8/H2O2 coreactants system, benefiting from the efficient peroxidase-like activity of the PtCo/CdS@GO toward H2O2, massive of transient reactive intermediates could react with K2S2O8, thus obtaining higher ECL emission. Therefore, the developed ECL immunosensor for anti-MPO detection displayed good analytical performance with good concentration linearity in the range of 0.02 to 1000 pg/mL and low detection limit down to 7.39 fg/mL.ConclusionsThe introduction of multi-function PtCo/CdS@GO luminophores into the established ECL immunoassay not only was successfully applied for specific detection of anti-MPO in clinical serum samples, but also provided a completely new concept to design other high-performance luminophores. Meaningfully, the ECL immunoassay strategy held wide potential for biomarkers detection in clinical diagnosis.Graphic abstract

Development of a rapid and sensitive quantum dot nanobead-based double-antigen sandwich lateral flow immunoassay and its clinical performance for the detection of SARS-CoV-2 total antibodies

Owing to the over-increasing demands in resisting and managing the coronavirus disease 2019 (COVID-19) pandemic, development of rapid, highly sensitive, accurate, and versatile tools for monitoring total antibody concentrations at the population level has been evolved as an urgent challenge on measuring the fatality rate, tracking the changes in incidence and prevalence, comprehending medical sequelae after recovery, as well as characterizing seroprevalence and vaccine coverage. To this end, herein we prepared highly luminescent quantum dot nanobeads (QBs) by embedding numerous quantum dots into polymer matrix, and then applied it as a signal-amplification label in lateral flow immunoassay (LFIA). After covalently linkage with the expressed recombinant SARS-CoV-2 spike protein (RSSP), the synthesized QBs were used to determine the total antibody levels in sera by virtue of a double-antigen sandwich immunoassay. Under the developed condition, the QB-LFIA can allow the rapid detection of SARS-CoV-2 total antibodies within 15 min with about one order of magnitude improvement in analytical sensitivity compared to conventional gold nanoparticle-based LFIA. In addition, the developed QB-LFIA performed well in clinical study in dynamic monitoring of serum antibody levels in the whole course of SARS-CoV-2 infection. In conclusion, we successfully developed a promising fluorescent immunological sensing tool for characterizing the host immune response to SARS-CoV-2 infection and confirming the acquired immunity to COVID-19 by evaluating the SRAS-CoV-2 total antibody level in the crowd.

A novel signal amplification label based on AuPt alloy nanoparticles supported by high-active carbon for the electrochemical detection of circulating tumor DNA

The detection of circulating tumor DNA (ctDNA) has increasingly received a great deal of attention considering its significance in cancer diagnosis. And the signal amplification plays an important role in the development of sensitive ctDNA biosensors. Herein, the nanocomposites (denoted as HAC-AuPt), integrating from high-active carbon (HAC) and AuPt alloy nanoparticles, were synthesized and subsequently used as a signal amplification label to fabricate a sandwich-type ctDNA electrochemical biosensor. Characterizations demonstrated that HAC presents uniform size distribution and AuPt alloy nanoparticles were successfully loaded on HAC. The current response could be amplified to a great extent by the resultant HAC-AuPt due to its excellent electrochemical property. The nanocomposites were further bounded with DNA signal probes (SPs) via Au-S or Pt-S assembly to form SPs-label. After the capture probes (CPs) were immobilized on the electrode surface, the target DNA (tDNA) and SPs-label were stepwise incubated on the CPs-modified electrode, thus forming a sandwich-type structure. By monitoring the catalytic signal of HAC-AuPt towards the reduction process of H2O2, this biosensor provided a wide linear range of 10−8 mol/L - 10−16 mol/L with a low detection limit of 3.6 × 10−17 mol/L (S/N = 3) for the detection of the tDNA. Furthermore, obvious differences in response signals among different DNAs were observed benefitting from the excellent selectivity of the biosensor. Besides, the long-term stability, reproducibility, and recovery rate were proved to be outstanding. These results indicate that the established biosensor holds a potential application in the clinical diagnosis of ctDNA.

Indirect competitive-structured electrochemical immunosensor for tetrabromobisphenol A sensing using CTAB-MnO2 nanosheet hybrid as a label for signal amplification.

Tetrabromobisphenol A (TBBPA) is a kind of brominated flame retardant that is usually added to products to reduce their flame retardancy. However, its extensive use has resulted in their residues being found in the environment, which is very harmful. Herein, an indirect competitive immunosensor has been established for TBBPA detection based on the signal amplification system. Pd nanospheres in situ reduced on the surface of MnO2 nanosheet hybrid (MnO2/Pd) was used as the label for the secondary antibody through the Pd-N bond, and gold-toluidine blue composite was loaded onto MWCNTs (MWCNTs/Au-TB), which functioned as the platform for the immunosensor. The spherical structure of Pd had abundant catalytic active sites, which enhanced the catalytic activity of MnO2/Pd as the label, hence amplifying the signal response. Besides, MWCNTs/Au-TB improved electron transfer and produced a strong signaling pathway for immobilizing antigens through the Au-NH2 bond, which can specifically recognize primary antibodies to improve sensitivity. The immunosensor had a linear concentration range of 0-81ng/mL, a low detection limit of 0.17ng/mL (S/N = 3), with good stability, selectivity, and reproducibility based on the above advantages. Additionally, the acceptable accuracy and recoveries (recoveries, 92-124%; CV, 3.3-8.8%) in the real water sample analysis indicated that this strategy is promising for emerging pollutant analysis.