Labels In Immunoassays Research Articles

Self-Assembled Perylene Diimide (PDI) Nanowire Sensitized In2O3@MgIn2S4 S-Scheme Heterojunction as Photoelectrochemical Biosensing Platform for the Detection of CA15-3.

Inorganic/organic heterojunctions show promising applications as high-performance sensing platforms for photoelectrochemical (PEC) immunosensors. This work reports constructing a PEC biosensor for CA15-3 based on a self-assembled perylene diimide (PDI) nanowire sensitized In2O3@MgIn2S4 S-scheme heterojunction platform. P-type semiconductor Cu2O nanoparticles were designed as a signal burst source and were used as immunoassay labels. The carboxyl group on self-assembled PDI nanowires eliminates the step of additional surface functionalization for covalent immobilization of the capture elements. The π-π stacking of PDI enhances electron generation efficiency, while the carboxylic acid groups on PDI promote electron transfer. The performance of the constructed sensor was validated using CA15-3 as a model. The experimental results showed that the sensor based on In2O3@MgIn2S4/PDI has excellent selectivity, stability, and reproducibility, and can sensitively detect CA15-3 in the range of 0.001-100 U·mL-1 with the detection limit of 0.00056 U·mL-1. The sensor has a broad application prospect. It is hoped that this research work based on the unique advantages of the organic compound PDI will inspire other researchers to design light-responsive materials and promote the development of the field of photoelectrochemical sensing.

Fluorescent Lateral Flow Immunoassay Based on Quantum Dots Nanobeads.

Quantum dots, also known as semiconductor nanocrystals, are novel fluorescent labels for biological imaging and sensing. However, quantum dot-antibody conjugates with small dimensions (~10 nm), prepared through laborious purification procedures, exhibit limited sensitivity in detecting certain trace disease markers using lateral flow immunoassay strips. Herein, we present a method for the preparation of quantum dot nanobeads (QDNB) using a one-step emulsion evaporation method. Using the as-prepared QDNB, a fluorescent lateral flow immunoassay was fabricated to detect disease biomarkers using C-reactive protein (CRP) as an example. Unlike single quantum dot nanoparticles, quantum dot nanobead-antibody conjugates are more sensitive as immunoassay labels due to signal amplification by encapsulating hundreds of quantum dots in one polymer composite nanobead. Moreover, the larger size of QDNBs facilitates easier centrifugation separation when conjugating QDNBs with antibodies. The fluorescent lateral flow immunoassay based on QDNBs was fabricated, and the CRP concentration in the sample was measured in 15 min. The test results can be qualitatively assessed under UV light illumination and quantitatively measured using a fluorescent reader within 15 min.

Characterization of nanozyme kinetics for highly sensitive detection.

Nanozymes have been widely used as enzyme substitutes. Based on a comprehensive literature survey of 261 publications, we report the significant differences in the Michaelis-Menten constants (Km) between peroxidase-mimicking nanozymes and horseradish peroxidase (HRP). Further, these differences were not considered in more than 60% of the publications for analytical developments. As a result, nanozymes' catalytic activity is limited, resulting in a potentially higher limit of detection (LOD). We used a peroxidase-mimicking Au@Pt nanozyme, which has Km for TMB comparable with HRP and three orders of magnitude higher Km for H2O2. Using the Au@Pt nanozyme as a label for immunoassays, non-optimized nanozyme substrate concentrations led to 30 times higher LOD compared to optimized conditions. The results confirm the necessity of measuring nanozymes' kinetic parameters and the corresponding adjustment of substrate concentrations for highly sensitive detection.

Nanoparticle-Based Bioaffinity Assays: From the Research Laboratory to the Market.

Advances in the development of new biorecognition elements, nanoparticle-based labels as well as instrumentation have inspired the design of new bioaffinity assays. This review critically discusses the potential of nanoparticles to replace current enzymatic or molecular labels in immunoassays and other bioaffinity assays. Successful implementations of nanoparticles in commercial assays and the need for rapid tests incorporating nanoparticles in different roles such as capture support, signal generation elements, and signal amplification systems are highlighted. The limited number of nanoparticles applied in current commercial assays can be explained by challenges associated with the analysis of real samples (e.g., blood, urine, or nasal swabs) that are difficult to resolve, particularly if the same performance can be achieved more easily by conventional labels. Lateral flow assays that are based on the visual detection of the red-colored line formed by colloidal gold are a notable exception, exemplified by SARS-CoV-2 rapid antigen tests that have moved from initial laboratory testing to widespread market adaption in less than two years.

Hierarchically Structured and Highly Dispersible MOF Nanozymes Combining Self-Assembly and Biomineralization for Sensitive and Persistent Chemiluminescence Immunoassay.

Metal-organic frameworks (MOF) are promising candidates for the construction of artificial nanozymes and have found applications in many fields. However, the preparation of nanosized MOF materials with high performance and good dispersibility is still a big challenge and is in great demand as signal labels for immunoassays. In this work, hierarchically structured and highly dispersible MOF nanoparticles were facilely prepared in a one-pot method. Self-assembled micelles from PEGylated hematin were used as structured templates to mediate the formation of zeolitic imidazole framework-8 (ZIF-8) nanoparticles in aqueous solution. The encapsulation of micelles in ZIF-8 frameworks produces well-dispersed nanoparticles and generates dual-confinement effects for catalytic hematin. Owing to the hierarchical structures, the formed MOF nanozymes show enhanced peroxidase-like activity and enable persistent chemiluminescence behaviors for the luminol system. Sandwich-type chemiluminescence immunoassays for carcinoembryonic antigen (CEA) were proposed using MOF nanozymes as signal labels, and good analytical performances were achieved. The combination of self-assembly and biomineralization may open new avenues for the development of MOF nanomaterials.

(Invited) Bio-Applications of Carbon Nanotubes for NIR Imaging Probes and Guided Bone Regeneration Membranes

Single-walled carbon nanotubes (CNTs) have been expected for biological and medical applications because of their unique optical and chemical properties. One of the promising applications is imaging probes because CNTs show fluorescence in the near-infrared (NIR) region, which is highly transparent for biomaterials. We have reported the synthesis method of the epoxide-type oxygen-doped CNTs (Ep-CNTs) and their application as a near-infrared fluorescent probe [1-3]. Treated (6, 5) nanotubes show photoluminescence at ~1280 nm, which corresponds to the most transparent regions for biomaterials [1]. Immunoassay and fluorescence vascular angiography of mice were demonstrated by using the produced Ep-CNTs as infrared fluorescent labels [1,3] and imaging agents [1,2], respectively. From a practical point of view, the biodistributions of the Ep-CNTs imaging probe after administration to mice were investigated in detail [2]. In addition, the biological responses of mice following administration, which are relevant to safety, were also introduced [2].More recently, we found that CNTs exhibit high compatibility with bone tissue [4]. The guided bone regeneration (GBR) technique is commonly applied to reconstruct alveolar bone and treat peri-implant bone defects. It was found that CNT-based membrane for GBR exhibits high strength to provide a space for bone formation and provide cellular shielding to induce osteogenesis.In this meeting, we will report above biological and medical applications of CNTs in detail.1. Y. Iizumi, M. Yudasaka, J. Kim, H. Sakakita, T. Takeuchi, T. Okazaki, Oxygen-doped carbon nanotubes for near-infrared fluorescent labels and imaging probes, Sci. Rep., 8, 6272 (2018).2. T. Takeuchi, Y. Iizumi, M. Yudasaka, S. K. Kondoh, T. Okazaki, Characterization and biodistribution analysis of oxygen-doped single-walled carbon nanotubes used as in vivo fluorescence imaging probes, Bioconjugate Chem., 30, 1323−1330 (2019). (Cover Article)3. K. Kojima, Y. Iizumi, M. Zhang, T. Okazaki, Streptavidin-conjugated oxygen-doped single-walled carbon nanotubes as near-infrared labels for immunoassays, Langmuir, 38, 1509-1513 (2022).4. Y. Xu, E. Hirata, Y. Iizumi, N. Ushijima, K. Kubota, S. Kimura, Y. Maeda, T. Okazaki, A. Yokoyama, Single-walled Carbon Nanotube Membranes Accelerate Active Osteogenesis in Bone Defects: Potential of Guided Bone Regeneration Membranes, ACS Biomater. Sci. Eng., 8, 1667-1675 (2022).

Express test for NT-proBNP competitive detection based on lateral flow immunoassay using silanized fluorescent quantum dots

This paper describes the step-by-step development and the application of a lateral flow immunoassay (LFIA) for the detection of the N-terminal pro-brain natriuretic peptide (NT-proBNP). NT-proBNP is widely used as a biomarker for diagnosing heart failure and other cardiac dysfunctions, distinguishing patients with heart failure from patients without heart failure, and for risk assessment. CdSe/CdS fluorescent quantum dots (QDs) were synthesized as immunoassay labels, carefully coated with a silicon dioxide shell with a high fluorescence quantum yield of 51% for silanized QDs, and finally functionalized with carboxy- or epoxy groups. The conjugation pathways of the resulting silanized QDs with antibodies specific to amino acid residues 61-76 in NT-proBNP were optimized. The LFIA uses the principle of competitive detection with the test line containing proBNP precursor molecule as the cover antigen and the control line containing rabbit anti-mouse immunoglobulins. All components of the LFIA strip, including membrane type, blocking buffer composition, and QD-antibody conjugate composition, were optimized to reduce nonspecific interaction. The LFIA test was applied to determine NT-proBNP in human plasma. The optimal dilution of plasma for application of the test was found to be 10-fold. Under optimized conditions, the LFIA cut-off level was set as 0.5 ng/mL NT-proBNP in human plasma. The LFIA design ensures that the test line fluorescence disappears at the cut-off concentration.

Photocurrent quenching by competitive consumption of surface electron donor and light absorption for immunosensing

This work designs a competitive consumption strategy of surface electron donor and light absorption for quenching the photocurrent of ZnSnO3 nanocubes/BiOI nanoarrays/polydopamine (ZnSnO3 NCs/BiOI NAs/PDA) as a photoactive material. This material can be formed on electrode surface by successive coating and deposition to provide a substrate for immobilization of capture antibody, and producing strong photocurrent in the presence of ascorbate acid as a surface electron donor due to the well matching structure of band gaps between ZnSnO3 NCs and BiOI NAs, the excellent light absorption ability and high photo-electron conversion efficiency of BiOI NAs and PDA, and the accelerated electron transfer. Using ascorbate oxidase loaded dopamine-melanin nanosphere (DAM-AAO) as a label of the signal (secondary) antibody, the sandwich-type immunoreaction leads to dual photocurrent quenching of the label through the competitive consumption of ascorbate acid with enzymatic oxidation and the light absorption by DAM nanosphere. Thus, a sensitive “On-Off” photoelectrochemical (PEC) immunosensing method is constructed for the analysis of neuron specific enolase (NSE). The proposed method shows a detection range of 0.1 pg/mL −50 ng/mL and a detection limit of 0.03 pg/mL. The excellent performance and the recovery text demonstrated the practicability of the designed strategy and label in immunoassay of different protein biomarkers.

Fluorescent Immunoassay with a Copper Polymer as the Signal Label for Catalytic Oxidation of O-Phenylenediamine.

This work suggested that Cu2+ ion coordinated by the peptide with a histidine (His or H) residue in the first position from the free N-terminal reveals oxidase-mimicking activity. A biotinylated polymer was prepared by modifying His residues on the side chain amino groups of lysine residues (denoted as KH) to chelate multiple Cu2+ ions. The resulting biotin-poly-(KH-Cu)20 polymer with multiple catalytic sites was employed as the signal label for immunoassay. Prostate specific antigen (PSA) was determined as the model target. The captured biotin-poly-(KH-Cu)20 polymer could catalyze the oxidation of o-phenylenediamine (OPD) to produce fluorescent 2,3-diaminophenazine (OPDox). The signal was proportional to PSA concentration from 0.01 to 2 ng/mL, and the detection limit was found to be eight pg/mL. The high sensitivity of the method enabled the assays of PSA in real serum samples. The work should be valuable for the design of novel biosensors for clinical diagnosis.

Iridium nanoclusters as high sensitive-tunable elemental labels for immunoassays: Determination of IgE and APOE in aqueous humor by inductively coupled plasma-mass spectrometry

Iridium nanoclusters (IrNCs) stabilized with citrate were synthesized and then the ligand was exchanged by lipoic acid (LA). The IrNCs@LA were bioconjugated through carbodiimide chemistry with specific antibodies to prepare IrNCs-labelled immunoprobes. The IrNCs-immunoprobes were employed in competitive immunoassays for immunoglobulin E (IgE) and apolipoprotein E (APOE) determination by detecting the iridium through inductively coupled plasma – mass spectrometry (ICP-MS). The IrNCs@LA have a 1.89 nm diameter at average and each NC contains 250 Ir atoms. Labelling of specific antibodies with IrNCs was optimized in terms of recognition capabilities and signal amplification by ICP-MS. Amplification and detection limits can be tuned by selecting the IrNCs:Ab molar ratio. An immunoprobe prepared by mixing a 10:1 IrNC:Ab molar ratio was selected for the determination of IgE and APOE in aqueous humor, achieving a signal amplification of 1760 iridium atoms per molecule of the sought protein and limits of detection in the tens of pg mL−1 of protein. The IrNCs-immunoprobes were evaluated for IgE determination in serum samples as well as for IgE and APOE in aqueous humor (from controls subjects and patients affected by primary open angle glaucoma) by ICP-MS, being required just sample dilution as pre-treatment. Results were corroborated with commercial ELISA kits.

Streptavidin-Conjugated Oxygen-Doped Single-Walled Carbon Nanotubes as Near-Infrared Labels for Immunoassays.

Single-walled carbon nanotubes (CNTs) are promising candidates for near-infrared (NIR) fluorescent labels in diagnostic fields. We report a complex of oxygen-doped CNT (o-CNT) and streptavidin (SA) for preparing CNT-based NIR labels with a high reaction efficiency in immunoassays. This complex specifically binds to biotin molecules by conjugating a linker molecule of phospholipid polyethylene glycol (PL-PEG) to SA (o-CNT-SA). The immunoprecipitation reaction efficiency between o-CNT-SA and biotin reaches 79.3% when the surface of o-CNTs is uniformly covered with SA-conjugated PL-PEG. The strong affinity between SA and biotin is useful for preparing CNT-based sensitive NIR fluorescent labels.

Point-of-care quantification of serum cellular fibronectin levels for stratification of ischemic stroke patients

The abundance of cellular fibronectin (c-Fn) for ischemic stroke patients and the narrow time-window (<4.5 h) for the decision to administer the thrombolytic treatment with recombinant tissue plasminogen activator (rtPA) are challenging for the development of a point-of-care (PoC) diagnostic platform. We report a case of stratification of ischemic stroke patients based on a magnetoresistive biosensor platform that quantifies the c-Fn levels in a small volume of serum, within the clinically relevant time-window. Our PoC platform uses different ratios of biofunctionalized magnetic nanoparticles (MNPs) as immunoassay labels to adjust the sensitivity within the clinically relevant ranges for c-Fn (1-4 μg/mL). After optimizing the detection range, resolution, and sensitivity, our device was able to stratify ischemic stroke patients who developed hemorrhagic transformation, the main side-effect of rtPA, from those (both non-treated and treated with rtPA) who did not.

Fluorescent AgInS/ZnS quantum dots microplate and lateral flow immunoassays for folic acid determination in juice samples.

Anoninstrumental rapid test for folic acid (FA) detection with visual results evaluation utilizing bright water-stable AgInS/ZnS (AIS/ZnS) quantum dots (QDs)is reported. AIS/ZnS QDs are hydrophilic photostable nanocrystals with size < 7nm and emission in the visible range. They were synthesized directly in the water phase by asimple method compared to the synthesis of other QDs and conjugated with monoclonal antibodies specific for FAvia ligand carboxyl groups. The conjugate was used for the development of instrumental qualitative and rapid quantitative FA detection methods. The competitive fluorescent microplate immunosorbent assay provided alimit of detection of 0.1ng/mL FAand half maximal inhibitory concentration (IC50) of24ng/mLFA. The analytical signal was measured at ʎex = 410nm and ʎem=590nm. The proposed method showed no cross-reaction with other group B vitamins. For FA screening in juice samples, the lateral flow immunoassay was developed with avisual cutoff levelof 3μg/mL. In our perception, the developed methods are convenient for proving the perception of the AIS/ZnS QDs application as a luminescent label for immunoassay and are effective for FA detection. Graphical abstract.

Fluorescence immunoassay based on nitrogen doped carbon dots for the detection of human nuclear matrix protein NMP22 as biomarker for early stage diagnosis of bladder cancer

A selective, fast acting and eco–friendly fluorescence immunoassay technique based on Nitrogen doped carbon dots (NCDs) is proposed for the detection of Nuclear Matrix Protein 22 (NMP22, antigen). Via the hydrothermal method and with the use of citric acid and urea, we synthesized NCDs with high quantum yield. Monoclonal antibodies (mAb, antibody) were labeled with NCDs through the EDC–NHS amidization technique and, in order to carry out the immunoreaction between the antigen and antibody, the resulting NCDs –mAb conjugates were then incubated with a small amount of NMP22). The established immunocomplex on the carboxylated NCDs led to the quenching of the fluorescence intensity. Under optimal conditions, a linear correlation between the change in fluorescence intensity and NMP22 concentration in the range of 1.3–16.3 ng/mL was observed and a detection limit of 0.047 ng/mL (47 pg/mL) was attained. This detection method was successfully able to determine NMP22 in human urine samples, with recoveries ranging from 96.50% to 103.61%. These results provide ample proof regarding the potential use of NCDs as fluorescence labels in immunoassays.

Quinone-based antibody labeling reagent for enzyme-free chemiluminescent immunoassays. Application to avidin and biotinylated anti-rabbit IgG labeling

Chemiluminescence-enzyme immunoassays make it possible to measure trace components with high sensitivity and selectivity due to the high specificity of the antigen-antibody reaction and the high sensitivity of chemiluminescence assays. However, using an enzyme-labeled antibody suffers from many problems such as low reproducibility due to the instability of the enzyme and inhibition of antigen-antibody reaction due to its steric effect. Therefore, herein we report an innovative non-enzymatic chemiluminescence immunoassays labeling reagent through using quinone as a signal-generating tag coupled with biotin as a binder, to overcome enzymatic labeling problems. Biotinylated-1,4-naphthoquinone (biotin-NQ) was synthesized and characterized and it could produce long-lasting chemiluminescence upon mixing with dithiothreitol and luminol based on the redox cycle of quinone. Biotin-NQ showed exceptional stability towards different stress factors that may be encountered during performing the immunoassay such as high temperatures, highly acidic and alkaline conditions, and repeated freeze-thaw cycles. On the other hand, all these conditions lead to decreased labeling enzyme reactivity due to possible denaturation of its protein structure. Finally, the measurement of the biotin-labeled antibody was successfully performed using biotin-NQ and avidin. As a result, the antibody could be detected down to 25.7 nM which is 2.5 times sensitive than biotin-HRP chemiluminescence-enzyme immunoassays. Moreover, our method was applied successfully for determination of avidin using immobilized biotinylated antibody and biotin-NQ, which simulates immunoassays. Avidin could be detected down to 23.4 nM with excellent linearity (r = 0.996). Accordingly, our developed reagent, biotin-NQ, could be used as a universal highly stable, cost-effective, and steric free non-enzymatic label for immunoassays.

Detection of E. coli labeled with metal-conjugated antibodies using lateral-flow assay and laser-induced breakdown spectroscopy.

This study explores the adoption of laser-induced breakdown spectroscopy (LIBS) for the analysis of lateral-flow immunoassays (LFIAs). Gold (Au) nanoparticles are standard biomolecular labels among LFIAs, typically detected via colorimetric means. A wide diversity of lanthanide-complexed polymers (LCPs) are also used as immunoassay labels but are inapt for LFIAs due to lab-bound detection instrumentation. This is the first study to show the capability of LIBS to transition LCPs into the realm of LFIAs, and one of the few to apply LIBS to biomolecular label detection in complete immunoassays. Initially, an in-house LIBS system was optimized to detect an Au standard through a process of line selection across acquisition delay times, followed by determining limit of detection (LOD). The optimized LIBS system was applied to Au-labeled Escherichia coli detection on a commercial LFIA; comparison with colorimetric detection yielded similar LODs (1.03E4 and 8.890E3 CFU/mL respectively). Optimization was repeated with lanthanide standards to determine if they were viable alternatives to Au labels. It was found that europium (Eu) and ytterbium (Yb) may be more favorable biomolecular labels than Au. To test whether Eu-complexed polymers conjugated to antibodies could be used as labels in LFIAs, the conjugates were successfully applied to E. coli detection in a modified commercial LFIA. The results suggest interesting opportunities for creating highly multiplexed LFIAs. Multiplexed, sensitive, portable, and rapid LIBS detection of biomolecules concentrated and labeled on LFIAs is highly relevant for applications like food safety, where in-field food contaminant detection is critical. Graphical abstract.

Bimodal determination of immunoglobulin E by fluorometry and ICP-MS by using platinum nanoclusters as a label in an immunoassay.

The authors describe the use of platinum nanoclusters (PtNCs) as bimodal labels in a competitive immunoassay for immunoglobulin E (IgE). Both fluorometry and inductively coupled plasma - mass spectrometry (ICP-MS) are used. Optimization of the PtNCs synthesis using lipoic acid as ligand was carried out. The time for synthesis and the effect of NaOH added to the PtNCs precursor mixture was optimized with the aim to obtain PtNCs with strong red fluorescence and low size dispersity. Maximal fluorescence was obtained at excitation/emission wavelengths of 455/620nm. The average diameter (1.5nm) and crystal structure (face-centered cubic structure) of the PtNCs were determined by HR-TEM. It was calculated that each PtNC contains 116 Pt atoms at average. Labelling of the antibody (Ab) against IgE with PtNCs was optimized in terms of recognition capabilities and fluorescence intensity. A molar ratio (Ab:PtNCs) of 1:11 is found to be best. A competitive immunoassay for IgE was developed and detection was carried out by using both ICP-MS (by measuring 195Pt) and fluorometry. The limit of detection (LOD) of the fluoroimmunoassay is 0.6ngmL-1 of IgE. The LOD of the ICP-MS method is as low as 0.08ngmL-1. The method was evaluated by analyzing four (spiked) serum samples by ICP-MS. No sample pretreatment excepting dilution is needed. Results compared favorably with those obtained by a commercial ELISA kit. Graphical abstract Schematic representation of the bimodal quantification (fluorescence and ICP-MS) of immunoglobulin E (Ig E) in human serum using antibody against human Ig E, labelled with several platinum nanoclusters (NCs) as immunoprobe. Elemental mass spectrometry (MS) allows high amplification of the signal because of the high number of platinum atoms per nanocluster (~116 Pt/NC).

Photostable methylene blue-loaded silica particles used as label for immunosorbent assay of Salmonella Typhimurium.

Salmonella Typhimurium is a major cause of food poisoning. To solve the limitations of the routine enzyme linked immunosorbent assay such as laborious assay procedure, lack of long-term enzyme stability, and insufficient sensitivity, we provided a non-enzymatic colorimetric immunosorbent assay platform to overcome these problems. The highly photostable redox dye particles was constructed by silica particles (diameter = 598±14.4 nm) loaded with methylene blue (Si-MB) and applied to be a label for immunoassay of S. Typhimurium. The sandwich assay format involved incubation of an analyte in a microplate wells modified with monoclonal anti-Salmonella, followed by exposure to a polyclonal anti-Salmonella/Si-MB bioconjugate and then measurement of absorbance at 598nm. The platform had an assay time of 20min, could detect heat-killed Salmonella with a limit of detection of 48CFU mL-1 , and gave good recoveries in milk. The labels could be stored at 4°C for 70 days without any deterioration.

Immunoassay for pathogenic bacteria using platinum nanoparticles and a hand-held hydrogen detector as transducer. Application to the detection of Escherichia coli O157:H7.

An innovative approach is presented for portable and sensitive detection of pathogenic bacteria. A novel synthetic hybrid nanocomposite encapsulating platinum nanoparticles, as a highly efficient catalyst, catalyzes thehydrolysis of the ammonia-borane complex to generate hydrogen gas. The nanocomposites are used as a label for immunoassays. A portable hand-held hydrogen detector combined with nanocomposite-induced signal conversion was applied for point-of-care testingofpathogenic bacteria. A hand-held hydrogen detector was used as the transducer. Escherichia coli O157:H7 (E. coli O157: H7), as detection target, formed a sandwich structure with magnetic beads and hybrid nanocomposites. Magnetic beads were used for separation of the sandwich structure, and hybrid nanocomposites as catalysts to catalyze the generation of hydrogen from ammonia-borane. The generated hydrogen was detected by a hydrogen detector using an electrochemical method. E. coli O157:H7 has a detection limit of 10CFU·mL-1. The immunosensor made the hand-held hydrogen detector a point-of-care meter to be used outdoors for the detection and quantification of targets beyond hydrogen. Graphical abstract Schematic presentation of one-pot synthetic peptide-Cu3(PO4)2 hybrid nanocomposites embedded PtNPs (PPNs), encapsulating many Pt particles. The PPNs acts as an ideal immunoprobe for hand-held H2 detector signal readouts, by transforming pathogenic bacteria recognition events into H2 signals.

In Situ Generation of Prussian Blue with Potassium Ferrocyanide to Improve the Sensitivity of Chemiluminescence Immunoassay Using Magnetic Nanoparticles as Label.

Using magnetic nanoparticles (MNPs) as a label in immunoassay (IA) possesses advantages such as high specific surface area, simple modification process. However, the catalytic activity of MNPs is low, which limits their applications in IA. The present study found it interesting that potassium ferrocyanide reacts with MNPs, leading to the in situ generation of Prussian blue. The produced Prussian blue shows high catalytic activity on a luminol chemiluminescent (CL) reaction. Therefore, a simple and sensitive immunoassay for rabbit IgG (rIgG) as model analyte using MNPs as label was developed. The CL intensity had a linear increase with the concentration of rIgG that ranged from 0.625 to 20 ng mL-1. The limit of detection was calculated to be 0.59 ng mL-1. In addition, the applicability of this method was evaluated using the standard addition method. The recovery ranged from 80.0% to 115.0%. What's more, the proposed CLIA method based on in situ generation of Prussian blue with MNPs was also applied to the detection of carcinoembryonic antigen (CEA) and hepatitis B virus (HBV)-related sequence-specific DNA. The LOD for the detection of CEA and sequence-specific DNA was estimated to be 0.28 ng mL-1 and 0.044 pmol, respectively.