Recent Advances in Electrochemical Immunosensors

Bioinspired superwettable electrodes towards electrochemical biosensing

Superwettable materials have attracted much attention due to their fascinating properties and great promise in several fields. Recently, superwettable materials have injected new vitality into electrochemical biosensors. Superwettable electrodes exhibit unique advantages, including large electrochemical active areas, electrochemical dynamics acceleration, and optimized management of mass transfer. In this review, the electrochemical reaction process at electrode/electrolyte interfaces and some fundamental understanding of superwettable materials are discussed. Then progress in different electrodes has been summarized, including superhydrophilic, superhydrophobic, superaerophilic, superaerophobic, and superwettable micropatterned electrodes, electrodes with switchable wettabilities, and electrodes with Janus wettabilities. Moreover, we also discussed the development of superwettable materials for wearable electrochemical sensors. Finally, our perspective for future research is presented.

Biomimetic Nanoscale Materials for Skin Cancer Therapy and Detection

Skin cancer has developed as one of the most common types of cancer in the world, with a significant impact on public health impact and the economy. Nanotechnology methods for cancer treatment are appealing since they allow for the effective transport of medicines and other biologically active substances to specific tissues while minimizing harmful consequences. It is one of the most significant fields of research for treating skin cancer. Various nanomaterials have been employed in skin cancer therapy. The current review will summarize numerous methods of treating and diagnosing skin cancer in the earliest stages. There are numerous skin cancer indicators available for the prompt diagnosis of this type of disease. Traditional approaches to skin cancer diagnosis are explored, as are their shortcomings. Electrochemical and optical biosensors for skin cancer diagnosis and management were also discussed. Finally, various difficulties concerning the cost and ease of use of innovative methods should be addressed and overcome.

Recent advances in the highly sensitive determination of zearalenone residues in water and environmental resources with electrochemical biosensors

Zearalenone (ZEN), a significant class of mycotoxin which is considered as a xenoestrogen, permits, similar to natural estrogens, it's binding to the receptors of estrogen resulting in various reproductive diseases especially, hormonal misbalance. ZEN has toxic effects on human and animal health as a result of its teratogenicity, carcinogenicity, mutagenicity, nephrotoxicity, genotoxicity, and immunotoxicity. To ensure water and environmental resources safety, precise, rapid, sensitive, and reliable analytical and conventional methods can be progressed for the determination of toxins such as ZEN. Different selective nanomaterial-based compounds are used in conjunction with different analytical detection approaches to achieve this goal. The current review demonstrates the state-of-the-art advances of nanomaterial-based electrochemical sensing assays including various sensing, apta-sensing and, immunosensing studies to the highly sensitive determination of various ZEN families. At first, a concise study of the occurrence, structure, toxicity, legislations, and distribution of ZEN in monitoring has been performed. Then, different conventional and clinical techniques and procedures to sensitive and selective sensing techniques have been reviewed and the efficient comparison of them has been thoroughly discussed. This study has also summarized the salient features and the requirements for applying various sensing and biosensing platforms and diverse immobilization techniques in ZEN detection. Finally, we have defined the performance of several electrochemical sensors applying diverse recognition elements couples with nanomaterials fabricated using various recognition elements coupled with nanomaterials (metal NPs, metal oxide nanoparticles (NPs), graphene, and CNT) the issues limiting development, and the forthcoming tasks in successful construction with the applied nanomaterials.

Veni, Vidi, Vici: Immobilized Peptide-Based Conjugates as Tools for Capture, Analysis, and Transformation

Analysis of peptide biomarkers of pathological states of the organism is often a serious challenge, due to a very complex composition of the cell and insufficient sensitivity of the current analytical methods (including mass spectrometry). One of the possible ways to overcome this problem is sample enrichment by capturing the selected components using a specific solid support. Another option is increasing the detectability of the desired compound by its selective tagging. Appropriately modified and immobilized peptides can be used for these purposes. In addition, they find application in studying the specificity and activity of proteolytic enzymes. Immobilized heterocyclic peptide conjugates may serve as metal ligands, to form complexes used as catalysts or analytical markers. In this review, we describe various applications of immobilized peptides, including selective capturing of cysteine-containing peptides, tagging of the carbonyl compounds to increase the sensitivity of their detection, enrichment of biological samples in deoxyfructosylated peptides, and fishing out of tyrosine–containing peptides by the formation of azo bond. Moreover, the use of the one-bead-one-compound peptide library for the analysis of substrate specificity and activity of caspases is described. Furthermore, the evolution of immobilization from the solid support used in peptide synthesis to nanocarriers is presented. Taken together, the examples presented here demonstrate immobilized peptides as a multifunctional tool, which can be successfully used to solve multiple analytical problems.

Responsive-released strategy based on lead ions-dependent DNAzyme functionalized UIO-66-NH2 for tumor marker

Signal labeling on electrode interface is an important step during the construction of immunosensor and most signal substances are directly affixed on the immunoprobe or substrate so that some problems such as flimsy labeling method and interference of insulating proteins on electrode surface have been existed to affect their readout. In order to solve above problems in electrochemical immunoassay, a lead ions-decodable autocephalous signal integrator based on UIO-66-NH₂ was proposed for the detection of prostate specific antigen (PSA). Briefly, a lead ions-dependent DNAzyme functionalized UIO-66-NH₂, in which methylene blue was encapsulated, was independently dispersed in solution phase to be closely associated with the lead sulfide labeled sandwich bioconjugates, and internal methylene blue molecules can be sustained released once a cationic exchange reaction was occurred between lead sulfide label and adscititious silver ions. Based on this designing, immunoassay for PSA was effectively connected with the dynamic behavior of methylene blue molecules through the cleavage of DNAzyme on MOFs surface and performed a wide linear range from 1 pg mL^-1 to 10 ng mL^-1 and a satisfactory detection limit with 0.34 pg mL^-1. The proposed strategy was expected to offer more valuable information for the application of MOFs in early and accurate cancer diagnosis.

Peptide-Based Electrochemiluminescence Biosensors Using Silver Nanoclusters as Signal Probes and Pd-Cu2O Hybrid Nanoconcaves as Coreactant Promoters for Immunoassays

Metal nanoclusters (NCs) possess high light stability and biocompatibility because of their unique quantum size effect, which has gradually become a new type of electrochemiluminescence (ECL) nanomaterial for immunoassays. However, the luminescence efficiency of metal NCs is too low to meet the needs of trace analysis, which limits its application. Herein, Ag NCs served as signal probes and Pd-Cu₂O hybrid nanoconcaves served as coreaction promoters, developing a highly efficient peptide-based biosensor for neuron-specific enolase (NSE) detection. Utilizing the reversible cycle of Cu⁺/Cu²⁺ and the reduction characteristics of Pd NPs, Pd-Cu₂O greatly accelerates the reduction of S₂O₈^2-. Meanwhile, Pd-Cu₂O has good hydrogen evolution activity, which promotes the generation of oxygen by improving the redox efficiency of the overall reaction, thus increasing the yield of active intermediates (OH^•) to promote the reduction of S₂O₈^2-. Specially, this is an effective attempt to use the hydrogen evolution reaction (HER) to accelerate the ECL emission of the S₂O₈^2- system. In addition, a short peptide ligand (NARKFYKGC, NFC) was developed to implement the targeted immobilization of antibodies, which can specifically bind to the Fc fragment of antibodies, thereby avoiding the occupation of the antigen binding site (Fab fragment). The introduction of NFC not only improves the binding efficiency of antibodies but also protects its bioactivity, thus significantly improving the sensitivity of the biosensor. Based on these strategies, the proposed biosensor provides a new perspective for the applications of metal NCs in ECL systems.

Biosensor-based assay of exosome biomarker for early diagnosis of cancer

Cancer imposes a severe threat to people's health and lives, thus pressing a huge medical and economic burden on individuals and communities. Therefore, early diagnosis of cancer is indispensable in the timely prevention and effective treatment for patients. Exosome has recently become an attractive cancer biomarker in noninvasive early diagnosis because of the unique physiology and pathology functions, which reflects remarkable information regarding the cancer microenvironment, and plays an important role in the occurrence and evolution of cancer. Meanwhile, biosensors have gained great attention for the detection of exosomes due to their superior properties, such as convenient operation, real-time readout, high sensitivity, and remarkable specificity, suggesting promising biomedical applications in the early diagnosis of cancer. In this review, the latest advances of biosensors regarding the assay of exosomes were summarized, and the superiorities of exosomes as markers for the early diagnosis of cancer were evaluated. Moreover, the recent challenges and further opportunities of developing effective biosensors for the early diagnosis of cancer were discussed.

Electrochemical Affinity Assays/Sensors: Brief History and Current Status

The advent of electrochemical affinity assays and sensors evolved from pioneering efforts in the 1970s to broaden the field of analytes accessible to the selective and sensitive performance of electrochemical detection. The foundation of electrochemical affinity assays/sensors is the specific capture of an analyte by an affinity element and the subsequent transduction of this event into a measurable signal. This review briefly covers the early development of affinity assays and then focuses on advances in the past decade. During this time, progress on electroactive labels, including the use of nanoparticles, quantum dots, organic and organometallic redox compounds, and enzymes with amplification schemes, has led to significant improvements in sensitivity. The emergence of nanomaterials along with microfabrication and microfluidics technology enabled research pathways that couple the ease of use of electrochemical detection for the development of devices that are more user friendly, disposable, and employable, such as lab-on-a-chip, paper, and wearable sensors.

Electrochemical Immunosensors for Quantification of Procalcitonin: Progress and Prospects

Human procalcitonin (PCT) is a peptide precursor of the calcium-regulating hormone calcitonin. Traditionally, PCT has been used as a biomarker for severe bacterial infections and sepsis. It has also been recently identified as a potential marker for COVID-19. Normally, serum PCT is intracellularly cleaved to calcitonin, which lowers the levels of PCT (<0.01 ng/mL). In severe infectious diseases and sepsis, serum PCT levels increase above 100 ng/mL in response to pro-inflammatory stimulation. Development of sensors for specific quantification of PCT has resulted in considerable improvement in the sensitivity, linear range and rapid response. Among the various sensing strategies, electrochemical platforms have been extensively investigated owing to their cost-effectiveness, ease of fabrication and portability. Sandwich-type electrochemical immunoassays based on the specific antigen–antibody interactions with an electrochemical transducer and use of nanointerfaces has augmented the electrochemical response of the sensors towards PCT. Identification of a superior combination of electrode material and nanointerface, and translation of the sensing platform into flexible and disposable substrates are under active investigation towards development of a point-of-care device for PCT detection. This review provides an overview of the existing detection strategies and limitations of PCT electrochemical immunosensors, and the emerging directions to address these lacunae.

Electrochemical Immunosensors with PQQ-Decorated Carbon Nanotubes as Signal Labels for Electrocatalytic Oxidation of Tris(2-carboxyethyl)phosphine

Nanocatalysts are a promising alternative to natural enzymes as the signal labels of electrochemical biosensors. However, the surface modification of nanocatalysts and sensor electrodes with recognition elements and blockers may form a barrier to direct electron transfer, thus limiting the application of nanocatalysts in electrochemical immunoassays. Electron mediators can accelerate the electron transfer between nanocatalysts and electrodes. Nevertheless, it is hard to simultaneously achieve fast electron exchange between nanocatalysts and redox mediators as well as substrates. This work presents a scheme for the design of electrochemical immunosensors with nanocatalysts as signal labels, in which pyrroloquinoline quinone (PQQ) is the redox-active center of the nanocatalyst. PQQ was decorated on the surface of carbon nanotubes to catalyze the electrochemical oxidation of tris(2-carboxyethyl)phosphine (TCEP) with ferrocenylmethanol (FcM) as the electron mediator. With prostate-specific antigen (PSA) as the model analyte, the detection limit of the sandwich-type immunosensor was found to be 5 pg/mL. The keys to success for this scheme are the slow chemical reaction between TCEP and ferricinum ions, and the high turnover frequency between ferricinum ions, PQQ. and TCEP. This work should be valuable for designing of novel nanolabels and nanocatalytic schemes for electrochemical biosensors.

Electrochemical microgap immunosensors for selective detection of pathogenic Aspergillus niger

Aspergillus niger (A. niger) is a well-known allergenic, harmful fungus in the indoor environment that can cause asthmatic symptoms and atopy. Previous immunosensing approach suffers from an insufficient detection limit, mainly because there are no techniques for target amplification. We report an electrochemical immunosensor that selectively quantifies the A. niger based on the detection of extracellular proteins by using a specific interaction with antibody. The sensor was designed to show a decrease in redox current upon binding of the antigens secreted from A. niger onto an antibody-immobilized surface between the interdigitated electrodes. The extracellular proteins were profiled by LC-MS/MS to identify the antigens existing in the A. niger solution. Since the targets of the sensor are the proteins, its sensitivity and selectivity remain almost intact even after filtration of the spores. It was also found that the use of secretion promoter in the sampling stage greatly improved the sensor's limit of detection (LOD) for the spores. By this, the LOD was lowered by a few orders of magnitude so as to reach the value as low as ~10¹ spores/mL.

The preparation of bifunctional hybrid nano-flowers and their application in the enzyme-linked immunosorbent assay for Helicobacter pylori detection

As the infection by Helicobacter pylori (H. pylori, HP) remains for a lifetime and may induce diseases such as gastric cancer, it is vital to detect and diagnose it. A new non-invasive indirect enzyme-linked immunosorbent assay (iELISA) method based on nano-flowers (NFs) is very advantageous for the sensitive detection of HP. Furthermore, the established iELISA method based on the organic-inorganic bifunctional hybrid nano-flowers including rabbit polyclonal antibody of HP labeled with peroxidase from horseradish (R-HP-Ab-HRP@Cu2+ NFs) showed linearity with HP at a concentration of 0-105 CFU mL-1 (R2 = 0.9997). Moreover, the limit of detection (LOD) reached 50 CFU mL-1, and not only was the detection sensitivity 20 times higher than that based on rabbit polyclonal antibody of HP labeled with peroxidase from horseradish (R-HP-Ab-HRP) but also the stability of R-HP-Ab-HRP in NFs was improved. In addition, the OD450 nm value was still linearly related to the concentration of HP at a range of 0-105 CFU mL-1 (R2 = 0.9952) with a LOD of 50 CFU mL-1 in an artificial saliva system. This study provided a sensitive, low-cost and convenient method for the non-invasive detection of HP.

Rapid electrochemical detection of Escherichia coli using nickel oxidation reaction on a rotating disk electrode

A standalone electrochemical method for detecting the bacterium Escherichia coli in water was developed using a nickel electrode and no biorecognition element. Electric current responses from different E. coli concentrations were recorded based on their interaction with a locally formed electrocatalyst. A rotating disk electrode was used to minimize the mass transport limitations at the interface. Results from experiments with the rotating disk electrode also paved the way for hypothesizing the detection mechanism. The operating conditions were established for sensing the electric current responses in the presence of E. coli. The least-squares linear regression model was fit to the data obtained from currents of some known E. coli concentrations. This probe had a detection limit in the order of 104 CFU/ml. The response time to detect the presence/absence of E. coli was less than half a second, while the total assay time, including quantification of its concentration, was 10 min. The electric current response from a solution mixed with E. coli and S. aureus showed current similar to E. coli only solution indicating the specificity of the sensor to respond to signals from E. coli. This electrochemical microbial sensor's uniqueness lies in its ability to rapidly detect E. coli by forming the catalyst locally on demand without the attachment of biorecognition elements.

Exosomal analysis: Advances in biosensor technology

Exosomes, a subtype of extracellular vesicle secreted by cells, have been a subject of intense research interest. Unfortunately, a simple and reliable method to separate exosomes has yet to be developed. As can be expected, the lack of a standardized method for extraction and purification has contributed to suboptimal inter-laboratory correlation and difficulty in comparison studies. Traditional techniques such as centrifugation, immunoaffinity and size exclusion chromatography, suffer from low purity and tend to be labor intensive thus making their use limited. To mitigate these drawbacks, an integrated biosensor-based exosome separation and detection has recently been developed. In this review, we examine five biosensors that use a variety of detection technology (colorimetric, fluorescent, surface plasmon resonance, surface-enhanced Raman scattering and electrochemical) and propose thoughts on standardization of exosomal analysis.

A simple electrochemical immunosensor based on worm-like platinum for highly sensitive determination of alpha-fetoprotein

Alpha-fetoprotein (AFP) has become a specific tumor marker of primary liver cancer in clinical diagnosis. In this work, we prepared worm-like platinum (WL Pt) nanomaterial via chemical etching without organic solvents and ultra-high temperature. Due to its small particle size and the formation of surface vacancies during the etching process, it had a large specific surface area, and thus exhibited superior electrocatalytic activity for the reduction of hydrogen peroxide. Combining the signal amplification based on hydrogen peroxide reduction and the specific recognition of antigen with antibody, we constructed a simple label-free electrochemical immunosensor with a sandwich-like structure. The developed electrochemical immunosensor showed a wide linear range (0.0001-100 ng mL^-1), a low detection limit (0.028 pg mL^-1), good selectivity and stability. Further, the immunosensor was comparable with enzyme-linked immunosorbent assay (ELISA) and had a good accuracy for AFP detection in human serum samples proving the feasibility of potential application, which is expect to become one of the most promising method in early diagnosis and clinical analysis for liver cancer.

Simple and Effective Approach to Prepare an Epoxy-Functionalized Polymer and Its Application for an Electrochemical Immunosensor

An epoxy-functionalized polymer based on a new skeleton has been prepared via an efficient method and it combined with aminated carbon nanotubes to form a new composite material. This new composite material was applied for the fabrication of an electrochemical immunosensor with good performance. The inexpensive and easily available IgG was used to test the performance of the prepared composite material. The levels of IgG were quantitatively analyzed using a differential pulse voltammetry detection system and the lowest detection limit was calculated to be 0.05 ng/mL. The detection system can also respond to IgG in the concentration range from 0.1 to 25 ng/mL.

Highly sensitive detection of caspase-3 activity based on peptide-modified organic electrochemical transistor biosensors

Caspase-3 is an important proteolytic enzyme that cleaves several key substrates in apoptotic processes, resulting in DNA fragmentation, the degradation of nuclear proteins, and the formation of apoptotic bodies. However, it is challenging to detect caspase-3 due to its low expression levels in cells. In this work, organic electrochemical transistors (OECTs) are used in the detection of caspase-3 for the first time. A self-assembled monolayer of the peptide is bonded to the Au gate electrode (GE) of an OECT via gold-sulphur bonds. It is found that the transfer curve of the transistor shifts to a lower gate voltage due to the modulation of the surface potential of the GE by the peptides. Then, the device is used in the detection of caspase-3 in aqueous solutions and shows a detection limit of 0.1 pM. Due to its high sensitivity, the device can detect caspase-3 in induced apoptotic HeLa cells. The system is low-cost, conveniently used and applicable for biological and medical monitoring where caspase-3 detection and quantification are required.

Cu2+-modified hollow carbon nanospheres: an unusual nanozyme with enhanced peroxidase-like activity

A Cu²⁺-modified carboxylated hollow carbon nanospheres (Cu²⁺-HCNSs-COOH) was designed with enhanced peroxidase-like activity for the detection of hydrogen peroxide (H₂O₂) and degradation of methylene blue (MB). Hollow polymer nanospheres were fabricated from aniline, pyrrole, Triton-100, and ammonium persulfate via confined interfacial copolymerization reaction, which can be pyrolyzed to create HCNSs with the hollow gap diameter of about 20 nm under high temperature. Combining the synergistic effect of coordination and electrostatic interaction, Cu²⁺-HCNSs-COOH was constructed by anchoring Cu²⁺ on the surface of HCNSs-COOH. Furthermore, Cu²⁺-HCNSs-COOH has higher affinity for 3,3',5,5'-tetramethylbenzidine and H₂O₂ of 0.20 mM and 0.88 mM, respectively. Based on the rapid response of Cu²⁺-HCNSs-COOH to H₂O₂, we constructed a colorimetric sensing platform by detecting the absorbance of the 3,3',5,5'-tetramethylbenzidine-H₂O₂ system at 652 nm for quantifying H₂O₂, which holds good linear relationship between 1 and 150 μM and has a detection limit of 0.61 μM. We also investigated the degradation of MB in the presence of Cu²⁺-HCNSs-COOH and H₂O₂, which can degrade 80.7% pollutants within 30 min. This research developed an unusual nanozyme for bioassays and water pollution treatment, which broadened the way for the rapid development of clinical diagnostics and water pollution treatment.

Multiplex Immunoassay Techniques for On-Site Detection of Security Sensitive Toxins

Biological toxins are a heterogeneous group of high molecular as well as low molecular weight toxins produced by living organisms. Due to their physical and logistical properties, biological toxins are very attractive to terrorists for use in acts of bioterrorism. Therefore, among the group of biological toxins, several are categorized as security relevant, e.g., botulinum neurotoxins, staphylococcal enterotoxins, abrin, ricin or saxitoxin. Additionally, several security sensitive toxins also play a major role in natural food poisoning outbreaks. For a prompt response to a potential bioterrorist attack using biological toxins, first responders need reliable, easy-to-use and highly sensitive methodologies for on-site detection of the causative agent. Therefore, the aim of this review is to present on-site immunoassay platforms for multiplex detection of biological toxins. Furthermore, we introduce several commercially available detection technologies specialized for mobile or on-site identification of security sensitive toxins.

Design and Analysis of a Sample-and-Hold CMOS Electrochemical Sensor for Aptamer-based Therapeutic Drug Monitoring

In this paper, we present the design and the analysis of an electrochemical circuit for measuring the concentrations of therapeutic drugs using structure-switching aptamers. Aptamers are single-stranded nucleic acids, whose sequence is selected to exhibit high affinity and specificity toward a molecular target, and change its conformation upon binding. This property, when coupled with a redox reporter and electrochemical detection, enables reagent-free biosensing with a sub-minute temporal resolution for in vivo therapeutic drug monitoring. Specifically, we design a chronoamperometry-based electrochemical circuit that measures the direct changes in the electron transfer (ET) kinetics of a methylene blue reporter conjugated at the distal-end of the aptamer. To overcome the high-frequency noise amplification issue when interfacing with a large-size (> 0.25 mm2) implantable electrode, we present a sample-and-hold (S/H) circuit technique in which the desired electrode potentials are held onto noiseless capacitors during the recording of the redox currents. This allows disconnecting the feedback amplifiers to avoid its noise injection while reducing the total power consumption. A prototype circuit implemented in 65-nm CMOS demonstrates a cell-capacitance-insensitive input-referred noise (IRN) current of 15.2 pArms at a 2.5-kHz filtering bandwidth. We tested our system in human whole blood samples and measured the changes in the ET kinetics from the redox-labeled aptamers at different kanamycin concentrations. By employing principal component analysis (PCA) to compensate for the sampling errors, we report a molecular noise floor (at SNR = 1) of 3.1 µM with sub 1-sec acquisition time at 0.22-mW power consumption.

Integrated Experimental and Theoretical Studies on an Electrochemical Immunosensor

Electrochemical immunosensors (EIs) integrate biorecognition molecules (e.g., antibodies) with redox enzymes (e.g., horseradish peroxidase) to combine the advantages of immunoassays (high sensitivity and selectivity) with those of electrochemical biosensors (quantitative electrical signal). However, the complex network of mass-transfer, catalysis, and electrochemical reaction steps that produce the electrical signal makes the design and optimization of EI systems challenging. This paper presents an integrated experimental and modeling framework to address this challenge. The framework includes (1) a mechanistic mathematical model that describes the rate of key mass-transfer and reaction steps; (2) a statistical-design-of-experiments study to optimize operating conditions and validate the mechanistic model; and (3) a novel dimensional analysis to assess the degree to which individual mass-transfer and reaction steps limit the EI's signal amplitude and sensitivity. The validated mechanistic model was able to predict the effect of four independent variables (working electrode overpotential, pH, and concentrations of catechol and hydrogen peroxide) on the EI's signal magnitude. The model was then used to calculate dimensionless groups, including Damkohler numbers, novel current-control coefficients, and sensitivity-control coefficients that indicated the extent to which the individual mass-transfer or reaction steps limited the EI's signal amplitude and sensitivity.

Immunosensor incorporating half-antibody fragment for electrochemical monitoring of amyloid-β fibrils in artificial blood plasma

In this report, an electrochemical immunosensor for the selective and sensitive monitoring of Aβ_1-42 fibrils is presented. The sensing platform was prepared by the formation of a 4,4'-thiobisbenzenethiol (TBBT) self-assembled monolayer on a clean gold surface followed by the covalent entrapment of gold nanoparticles (AuNPs). The half-antibody fragments of the Anti-Amyloid Fibrils antibody were immobilized on AuNPs via S-Au covalent bonds. Each step of immunosensor fabrication was characterized with cyclic voltammetry and electrochemical impedance spectroscopy. The biosensor was successfully used for the sensing of Aβ_1-42 fibrils in both phosphate saline buffer (PBS) and artificial blood plasma (ABP). The immunosensor sensitivity estimated based on calibration slopes was better in the presence of APP in the comparison to PBS. The LOD values obtained for both measuring media were of 0.6 pM level. The moderate response towards Aβ_1-42 oligomers demonstrated the immunosensor selectivity.

An electrochemiluminescence biosensor for p53 antibody based on Zn-MOF/GO nanocomposite and Ag+-DNA amplification

An ultrasensitive electrochemiluminescence biosensor was established based on the Zn-MOF/GO nanocomposite. Ag(I)-embedded DNA complexes were used as a signal amplification reagent. In this work, 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin (TCPP) and Zn²⁺ were integrated into a porphyrin paddlewheel framework (Zn-MOF) by a hydrothermal method. The synthesized Zn-MOF material has electrochemiluminescence property, and the luminescence intensity is improved after being composited with graphene oxide (GO). Based on the composite material, we constructed an ultrasensitive ECL biosensor for the p53 antibody detection. The composite material acted as an admirable substrate and then loaded plenty of p53 antigens to recognize the target (p53 antibody) accurately. Because of the bridging effect of streptavidin and biotin-conjugated goat anti-rabbit IgG (bio-ab2), the rich-C DNA with positive correlation with the target was modified on the electrode and then captured the co-reactant accelerator Ag⁺ to amplify the signal. Therefore, the ECL biosensor response increases with increasing p53 antibody concentration. In the range 0.1 fg/mL-0.01 ng/mL, the response signal of the biosensor has a good linear relationship with the p53 antibody concentration. The detection limit is 0.03 fg/mL (S/N = 3). Impressively, the biosensor not only featured high sensitivity, good stability, and excellent specificity for the detection of p53 antibody, but also provides a new way for early detection of cancer. Graphical abstract Schematic representation of the electrochemiluminescence sensor based on a Zn-MOF/GO nanocomposite, which can be applied to the determination of p53 antibody.

Label free Impedimetric Immunosensor for effective bladder Cancer detection in clinical urine samples

Galectin-1 protein has been recently recognized as a valuable urinary biomarker for the diagnosis and prognosis of bladder cancer. Herein, we present a sensitive and specific impedimetric immunosensor for the quantitative and label free detection of Galectin-1 protein in clinical urine samples. The immunosensor consists of nine gold interdigitated microelectrodes (3 × 3 array), which can simultaneously monitor multiple immunoreactions by analyzing the normalized impedance variations at each microelectrode during immunosensing. To obtain enhanced sensitivities, we have utilized Galectin-1/Al₂O₃ nanoprobes (Galectin-1 antibody conjugated to alumina nanoparticles) that can be selectively trapped on the microelectrode surface using positive dielectrophoresis (p-DEP). Preliminary studies highlight the feasibility of the proposed immunosensor for Gal -1 detection in T24 cell lysate spiked phosphate buffer saline and artificial urine samples with a limit of detection that is estimated to be in the pg/ml range. To verify its practical feasibility, we have tested the immunosensor for Galectin-1 detection in clinical urine samples obtained from normal patients and those diagnosed with bladder cancer. Analysis of the clinical tests shows that the median normalized impedance variation during immunosensing for 22 cancer patients and 26 normal patients is 27% and 10%, respectively, with an identified cutoff point of 19.5% above which the sensitivity and specificity of bladder cancer detection was 82.1% and 80.8%, respectively. Based on these results, the proposed immunosensor shows promise for bladder cancer diagnosis and prognosis in a point of care format, thus enabling improved public health monitoring.

Modification-free amperometric biosensor for the detection of wild-type p53 protein based on the in situ formation of silver nanoparticle networks for signal amplification

Sensitive and accurate quantification of wild-type p53 protein is of great importance for biological research and clinical diagnosis. Herein, a modification-free amperometric biosensor was proposed for sensitive detection of wild-type p53 protein by the signal amplification of silver nanoparticles (AgNPs) networks formed in situ on electrode surface. Double-stranded DNA (dsDNA) probe containing two consensus sites was immobilized on gold electrode surface to capture wild-type p53 protein. The cysteine thiol and amine groups on the exterior of the protein allowed for the attachment of bare AgNPs through the AgS or AgN interactions. Meanwhile, benzene-1,4-dithiol (BDT) molecules in solution triggered the assembly of more AgNPs on electrode surface through the AgS interactions, thus leading to the in situ formation of AgNPs networks for signal amplification. The target at the concentration as low as 0.1 pM can be readily determined. This method was further applied to determine wild-type p53 protein in spiked human serum and cell lysates with satisfactory results. Moreover, the biosensor is regenerative and does not require the modification of AgNPs with recognition element for signal readout. The modification-free strategy can potentially be applied to develop novel biosensors for detection of other biological macromolecules.

PdIrBP mesoporous nanospheres combined with superconductive carbon black for the electrochemical determination and collection of circulating tumor cells

An integrated electrochemical immunoassay is described for the determination of circulating tumor cells (CTCs). For the first time, Ketjen black (KB), which is a superconductive carbon material, was incorporated with Au nanoparticles (AuNPs) and used to modify the surface of gold electrodes. A cocktail of anti-epithelial cell adhesion molecules (EpCAM) and anti-vimentin antibodies was chosen to capture the CTCs. Palladium-iridium-boron-phosphorus alloy-modified mesoporous nanospheres (PdIrBPMNS) served as a catalytic tag to amplify the current signal. Glycine-HCl (Gly-HCl) was used as an antibody eluent to release and collect the captured CTCs from the electrodes for further clinical research without compromising cell viability. The response of the method increased linearly from 10 to 1 × 10⁶ cells mL^-1 CTCs, while the detection limit was calculated to be as low as 2 cells mL^-1. This method was successfully used to determine CTCs in spiked blood samples and demonstrated good recovery. Graphical abstractKetjen black/AuNPs was incorporated in the electrochemical platform to enhance the electron transfer ability of the electrode surface. PdIrBP mesoporous nanospheres were used to amplify DPV signal in this assay. The introduction of Gly-HCl realized nondestructive recovery of circulating tumor cells.

Translating in vitro diagnostics from centralized laboratories to point-of-care locations using commercially-available handheld meters

There is a growing demand for high-performance point-of-care (POC) diagnostic technologies where in vitro diagnostics (IVD) is fundamental for prevention, identification, and treatment of many diseases. Over the past decade, a shift of IVDs from the centralized laboratories to POC settings is emerging. In this review, we summarize recent progress in translating IVDs from centralized labs to POC settings using commercially available handheld meters. After introducing typical workflows for IVDs and highlight innovative technologies in this area, we discuss advantages of using commercially available handheld meters for translating IVDs from centralized labs to POC settings. We then provide comprehensive coverage of different signal transduction strategies to repurpose the commercially-available handheld meters, including personal glucose meter, pH meter, thermometer and pressure meter, for detecting a wide range of targets by integrating biochemical assays with the meters for POC testing. Finally, we identify remaining challenges and offer future outlook in this area.