Dual-Mode Electrochemical Immunoassay for Insulin Based on Cu7S4-Au as a Double Signal Indicator

Eco-Friendly Electrosynthesis of Cu-PANI-Pencil Composite: Enhanced Their Current Value, Acid Sensing, Click Chemistry and Turn On-Off Sunlight Photo-Catalytical H2O2 Activation

In this contribution, we report a straightforwardly and easily one-step synthesis of a small family of composites based in polyaniline grafted on HB2 graphite (PANI@UG) and their copper-doped derivatives (Cu50PANI@UG5-6). The PANI@UG composites were synthesized through electrochemical polymerization using cyclic voltammetry (CV) in three different acidic media: i) acetic acid (AcOH) at high and low concentration (12 and 1 M, using KCl as electrolytic support); ii) a mixture of AcOH and sulfuric acid (H2SO4, which have two roles: as electrolytic support and proton source) and iii) a mixture of acetonitrile (NCCH3) and H2SO4, under atmospheric conditions. Once the best conditions were achieved, our next step was focused on obtaining the Cu50PANI@UG5-6 composites using a solution of aniline and CuSO4 (50 mM) in AcOH:H2SO4 and NCCH3:H2SO4 solutions, respectively. All composites were characterized by CV, FT-IR, SEM and MALDI-TOF experiments. So, the current value was enhanced for the Cu50PANI@UG6 composite, which have three potential catalytical applications in: i) HClO4 acid sensing, ii) click chemistry and iii) sunlight drive photo-activation of H2O2.

A surface molecularly imprinted electrochemical biosensor for the detection of SARS-CoV-2 spike protein by using Cu7S4-Au as built-in probe

Sensitive detection of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) spike protein (S protein) is of significant clinical importance in the diagnosis of COVID-19 pandemic. In this work, a surface molecularly imprinted (SMI) electrochemical biosensor is fabricated for the detection of SARS-CoV-2 S protein. Cu₇S₄-Au is used as the built-in probe and modified on the surface of a screen-printed carbon electrode (SPCE). 4-Mercaptophenylboric acid (4-MPBA) is anchored to the surface of the Cu₇S₄-Au through Au-SH bonds, which can be used for the immobilization of the SARS-CoV-2 S protein template through boronate ester bonds. After that, 3-aminophenylboronic acid (3-APBA) is electropolymerized on the electrode surface and used as the molecularly imprinted polymers (MIPs). The SMI electrochemical biosensor is obtained after the elution of the SARS-CoV-2 S protein template with an acidic solution by the dissociation of the boronate ester bonds, which can be utilized for sensitive detection of the SARS-CoV-2 S protein. The developed SMI electrochemical biosensor displays high specificity, reproducibility and stability, which might be a potential and promising candidate for the clinical diagnosis of COVID-19.

Enhanced activation of H2O2 by bimetallic Cu2SnS3: A new insight for Cu (II)/Cu (I) redox cycle promotion

HYPOTHESIS

Despite that the development of Cu₂SnS₃ (CTS) catalyst has attracted increasing interests, few study has reported to investigate its heterogeneous catalytic degradation of organic pollutants in a Fenton-like process. Furthermore, the influence of Sn components towards Cu (II)/Cu (I) redox cycling in CTS catalytic systems remains a fascinating research.

EXPERIMENTS

In this work, a series of CTS catalysts with controlled crystalline phases were prepared via a microwave-assisted pathway and applied in the H₂O₂ activation for phenol degradation. The efficiency of phenol degradation in CTS-1/H₂O₂ system (CTS-1: the molar ratio of Sn (copper acetate) and Cu (tin dichloride) is determined to be Sn:Cu = 1:1) was systematically investigated by controlling various reaction parameters including H₂O₂ dosage, initial pH and reaction temperature. We discovered that Cu₂SnS₃ exhibited superior catalytic activity to the contrast monometallic Cu or Sn sulfides and Cu (I) acted as the dominant active sites. The higher Cu (I) proportions conduce to the higher catalytic activities of CTS catalysts. Quenching experiments and electron paramagnetic resonance (EPR) further proved that the activation of H₂O₂ by CTS catalyst produces reactive oxygen species (ROS) and subsequently leads to degradation of the contaminants. A reasonable mechanism of enhanced H₂O₂ activation in Fenton-like reaction of CTS/H₂O₂ system was proposed for phenol degradation by investigating the roles of copper, tin and sulfur species.

FINDINGS

The developed CTS acted as a promising catalyst in Fenton-like oxidation progress for phenol degradation. Importantly, the copper and tin species contribute to a synergetic effect for the promotion of Cu (II)/Cu (I) redox cycle, which thus enhanced the activation of H₂O₂. Our work may offer new insight on the facilitation of Cu (II)/Cu (I) redox cycle in Cu-based Fenton-like catalytic systems.

A Sandwich-Type Electrochemical Immunosensor for Insulin Detection Based on Au-Adhered Cu5 Zn8 Hollow Porous Carbon Nanocubes and AuNP Deposited Nitrogen-Doped Holey Graphene

Rapid, accurate, and sensitive insulin detection is crucial for managing and treating diabetes. A simple sandwich-type electrochemical immunosensor is engineered using gold nanoparticle (AuNP)-adhered metal-organic framework-derived copper-zinc hollow porous carbon nanocubes (Au@Cu₅ Zn₈ /HPCNC) and AuNP-deposited nitrogen-doped holey graphene (NHG) are used as a dual functional label and sensing platform. The results show that identical morphology and size of Au@Cu₅ Zn₈ /HPCNC enhance the electrocatalytic active sites, conductivity, and surface area to immobilize the detection antibodies (Ab₂ ). In addition, AuNP/NHG has the requisite biocompatibility and electrical conductivity, which facilitates electron transport and increases the surface area of the capture antibody (Ab₁ ). Significantly, Cu₅ Zn₈ /HPCNC exhibits necessary catalytic activity and sensitivity for the electrochemical reduction of H₂ O₂ using (i-t) amperometry and improves the electrochemical response in differential pulse voltammetry. Under optimal conditions, the immunosensor for insulin demonstrates a wide linear range with a low detection limit and viable specificity, stability, and reproducibility. The platform's practicality is evaluated by detecting insulin in human serum samples. All these characteristics indicate that the Cu₅ Zn₈ /HPCNC-based biosensing strategy may be used for the point-of-care assay of diverse biomarkers.

Signal On-Off Electrochemical Sensor for Glutathione Based on a AuCu-Decorated Zr-Containing Metal-Organic Framework via Solid-State Electrochemistry of Cuprous Chloride

A novel signal on-off glutathione (GSH) electrochemical sensor was developed based on a AuCu bimetal-decorated Zr-containing metal-organic framework (Zr-MOF), in which a signal amplification strategy promoted by solid-state electrochemistry of cuprous chloride (CuCl) was used. The Zr-MOF with a large surface area can be effectively used as the substrate for the in situ growth of AuCu bimetals to obtain the Zr-MOF@AuCu nanocomposite. The interaction between Cu in Zr-MOF@AuCu and Cl^- in the solution accompanied with the formation of CuCl displays an enlarged stable oxidation current, which greatly declines with the addition of GSH owing to the specific Cu-GSH interaction. The conversion of CuCl into Cu-GSH triggered the "crowding-out effect" and resulted in a sharp drop in the peak current of CuCl, which can realize the ultrasensitive and selective detection of GSH. The detection mechanism was investigated, and the detection range was 10 pM-1 mM with the detection limit as low as 2.67 pM. The special response mechanism for the detection of GSH allows the highly selective detection of GSH in various real samples with reliable results, endowing the proposed electroanalysis sensor with broad application prospects in biological and food analysis.

MOF-Derived Cu-BTC Nanowire-Embedded 2D Leaf-like Structured ZIF Composite-Based Aptamer Sensors for Real-Time In Vivo Insulin Monitoring

Insulin, which is a hormone produced by the β-cells of the pancreas, regulates the glucose levels in the blood and can transport glucose into cells to produce glycogen or triglycerides. Insulin deficiency can lead to hyperglycemia and diabetes. Therefore, insulin detection is critical in clinical diagnosis. In this study, disposable Au electrodes were modified with copper(II) benzene-1,3,5-tricarboxylate (Cu-BTC)/leaf-like zeolitic imidazolate framework (ZIF-L) for insulin detection. The aptamers are easily immobilized on the Cu-BTC/ZIF-L composite by physical adsorption and facilitated the specific interaction between aptamers and insulin. The Cu-BTC/ZIF-L composite-based aptasensor presented a wide linear insulin detection range (0.1 pM to 5 μM) and a low limit of detection of 0.027 pM. In addition, the aptasensor displayed high specificity, good reproducibility and stability, and favorable practicability in human serum samples. For the in vivo tests, Cu-BTC/ZIF-L composite-modified electrodes were implanted in non-diabetic and diabetic mice, and insulin was quantified using electrochemical and enzyme-linked immunosorbent assay methods.

Efficient photothermal and photodynamic synergistic antibacterial therapy of Cu7S4 nanosheets regulated by facet engineering

The surface arrangements of nanomaterials can regulate their electronic structure, which will tune physicochemical properties of materials to various applications. In this study, two Cu₇S₄ nanosheets with (304) and (224) exposed facets were synthesized, respectively, and their antibacterial activity of different facets for replacing antibiotics to solve seriously drug-resistant bacteria were further measured. Experimental and theoretical computation results unveiled that Cu₇S₄ with (224) exposed facet exhibited excellent antibacterial activity through synergetic photodynamic and photothermal therapy against Gram-positive Bacillus subtilis, Gram-negative Escherichia coli and drug-resistant Pseudomonas aeruginosa under near-infrared light (808 nm) irradiation. Furthermore, the antibacterial agents strongly inhibit mouse skin infection by drug-resistant Pseudomonas aeruginosa cells. The findings provide an efficient antibacterial strategy and might advance the method of designing and producing highly effective antibacterial nanomaterials through facet engineering.

Clinical Evaluation of a Novel Insulin Immunosensor

BACKGROUND

The estimation of available active insulin remains a limitation of automated insulin delivery systems. Currently, insulin pumps calculate active insulin using mathematical decay curves, while quantitative measurements of insulin would explicitly provide person-specific PK insulin dynamics to assess remaining active insulin more accurately, permitting more effective glucose control.

METHODS

We performed the first clinical evaluation of an insulin immunosensor chip, providing near real-time measurements of insulin levels. In this study, we sought to determine the accuracy of the novel insulin sensor and assess its therapeutic risk and benefit by presenting a new tool developed to indicate the potential therapeutic consequences arising from inaccurate insulin measurements.

RESULTS

Nine adult participants with type-1 diabetes completed the study. The change from baseline in immunosensor-measured insulin levels was compared with values obtained by standard enzyme-linked immunosorbant assay (ELISA) after preprandial injection of insulin. The point-of-care quantification of insulin levels revealed similar temporal trends as those from the laboratory insulin ELISA. The results showed that 70% of the paired immunosensor-reference values were concordant, which suggests that the patient could take action safely based on insulin concentration obtained by the novel sensor.

CONCLUSIONS

This proposed technology and preliminary feasibility evaluation show encouraging results for near real-time evaluation of insulin levels, with the potential to improve diabetes management. Real-time measurements of insulin provide person-specific insulin dynamics that could be used to make more informed decisions regarding insulin dosing, thus helping to prevent hypoglycemia and improve diabetes outcomes.

A novel electrochemical insulin aptasensor: From glassy carbon electrodes to disposable, single-use laser-scribed graphene electrodes

Insulin, a peptide hormone secreted by pancreatic β cells, affects the development of diabetes and associated complications. Herein, we propose an electrochemical aptasensor for sensitive and selective detection of insulin using laser-scribed graphene electrodes (LSGEs). Before using disposable LSGEs, the development and proof-of-concept sensing experiments were firstly carried out on research-grade glassy carbon electrode (GCE). The aptasensor is based on using Exonuclease I (Exo I) that catalyses the hydrolysis of single-stranded aptamers attached to the electrode surface; however, the hydrolysis does not occur if the insulin is bound to the aptamer. Therefore, the unbound aptamers are cleaved by Exo I while insulin-bound aptamers remain on the electrode surface. In the next step, the gold nanoparticle - aptamer (AuNPs-Apt) probes are introduced to the electrode surface to form a 'sandwich' structure with the insulin on the surface-attached aptamer. The redox probe, methylene blue (MB), intercalates into the aptamers' guanine bases and the sandwich structure of AuNPs-Apt/insulin/surface-bound aptamer amplifies electrochemical signal from MBs. The signal can be well-correlated to the concentrations of insulin. A limit of detection of 22.7 fM was found for the LSGE-based sensors and 9.8 fM for GCE-based sensors used for comparison and initial sensor development. The results demonstrate successful fabrication of the single-use and sensitive LSGEs-based sensors for insulin detection.

Electrochemical immunosensor based on hollow porous Pt skin AgPt alloy/NGR as a dual signal amplification strategy for sensitive detection of Neuron-specific enolase

Neuron-specific enolase (NSE) is a specific marker for small cell carcinoma (SCLC). Sandwich-type electrochemical immunosensors are powerful for biomarker analysis, and the electrocatalytic activity of the signal amplification platform and the performance of the substrate are critical to their sensitivity. In this work, N atom-doped graphene functionalized with hollow porous Pt-skin Ag-Pt alloy (HP-Ag/Pt/NGR) was designed as a dual signal amplifier. The hollow porous Pt skin structure improves the atomic utilization and the larger internal cavity spacing significantly increases the number of electroactive centers, thus exhibiting more extraordinary electrocatalytic activity and durability for H₂O₂ reduction. Using NGR with good catalytic activity as the support material of HP-Ag/Pt, the double amplification of the current signal is realized. For the substrate, polypyrrole-poly(3,4-ethylenedioxythiophene) (PPy-PEDOT) nanotubes were synthesized by a novel chemical polymerization route, which effectively increased the interfacial electron transfer rate. By coupling Au nanoparticles (Au NPs) with PPy-PEDOT, the immune activity of biomolecules is maintained and the conductivity is further enhanced. Under optimal conditions, the linear range was 50 fg mL^-1 - 100 ng mL^-1, and the limit of detection (LOD) was 18.5 fg mL^-1. The results confirm that the developed immunosensor has great promise for the early clinical diagnosis of SCLC.

Development of a Novel Insulin Sensor for Clinical Decision-Making

BACKGROUND

Clinical decision support systems that incorporate information from frequent insulin measurements to enhance individualized diabetes management remain an unmet goal. The development of a disposable insulin strip for fast decentralized point-of-care detection replacing the current centralized lab-based methods used in clinical practice would be highly desirable to improve the establishment of individual insulin absorption patterns and algorithm modeling processes.

METHODS

We carried out the development and optimization of a novel decentralized disposable insulin electrochemical sensor focusing on obtaining high analytical and operational performance toward achieving a true point-of-care insulin testing device for clinical on-site application.

RESULTS

Our novel insulin immunosensor demonstrated an attractive performance and efficient user-friendly operation by providing high sensitivity capability to detect endogenous and analog insulin with a limit of detection of 30.2 pM (4.3 µiU/mL), rapid time-to-result, stability toward remote site application, and scalable low-cost fabrication with an estimated cost-of-goods for disposable consumables of below $5, capable of near real-time insulin detection in a microliter (≤10 µL) sample droplet of undiluted serum within 30 minutes.

CONCLUSIONS

The results obtained in the optimization and characterization of our novel insulin sensor illustrate its suitability for its potential application in remote clinical environments for frequent insulin monitoring. Future work will test the insulin sensor in a clinical research setting to assess its efficacy in individuals with type 1 diabetes.

The TDs/aptamer cTnI biosensors based on HCR and Au/Ti3C2-MXene amplification for screening serious patient in COVID-19 pandemic

The accurate assay of cardiac troponin I (cTnI) is very important for acute myocardial infarction (AMI), it also can be employed as an effective index for screening serious patients in COVID-19 pandemic before fatal heart injury to reduce the mortality. A ratiometric sensing strategy was proposed based on electrochemiluminescent (ECL) signal of doxorubicin (Dox)-luminol or the electrochemical (EC) signal of methylene blue (MB) vs. referable EC signal of Dox. The bio-recognitive Tro4-aptamer ensures the high specificity of the sensor by affinity binding to catch cTnI, and the tetrahedral DNA (TDs) on Au/Ti₃C₂-MXene built an excellent sensing matrix. An in situ hybrid chain reaction (HCR) amplification greatly improved the sensitivity. The ratiometric sensing responses ECL_Dox-luminol/Current_Dox or Current_MB/Current_Dox linearly regressed to cTnI concentration in the range of 0.1 fM-1 pM or 0.1 fM-500 fM with the limit of detection (LOD) as 0.04 fM or 0.1 fM, respectively. Served as the reference signal, Current_Dox reflected the variation of sensor, it is very effective to ensure the accuracy of detection to obviate the false results. The proposed biosensors show good specificity, sensitivity, reproducibility and stability, have been applied to determine cTnI in real samples with satisfactory results. They are worth looking forward to be used for screening serious patient of COVID-19 to reduce the mortality, especially in mobile cabin hospital.

Triple-signaling amplification strategy based electrochemical sensor design: boosting synergistic catalysis in metal-metalloporphyrin-covalent organic frameworks for sensitive bisphenol A detection

A covalent organic framework (COF) is a promising type of porous material with customizable surface characteristics. Confining multiple catalytic units within a mesoporous COF can generate abundant active sites and improve the catalytic performance. In this work, a COF with both metalloporphyrin and a metal nanoparticle complex denoted as hemin/TAPB-DMTP-COF/AuNPs (TAPB: 1,3,5-tris(4-amino-phenyl)benzene, DMTP: 2,5-dimethoxyterephaldehyde, AuNPs: Au nanoparticles) has been successfully fabricated through a hierarchical encapsulation method. The as-synthesized composite was then employed to construct an electrochemical sensing platform for the efficient detection of bisphenol A (BPA). Under the optimal conditions, the hemin/TAPB-DMTP-COF/AuNP sensor presented a linear range of 0.01-3 μmol L^-1 and a low detection limit of 3.5 nmol L^-1. The satisfactory signal amplification is based on a triple-signaling amplification strategy due to the abundant Fe³⁺ sites of Fe-porphyrin, high conductivity of AuNPs and a large specific surface area of the TAPB-DMTP-COF. The proposed method was used to measure the content of BPA in different water samples with a satisfactory recovery from 95.5 to 104.0%, suggesting the great potential of the sensor in practical applications.

MWCNTs-CoP hybrids for dual-signal electrochemical immunosensing of carcinoembryonic antigen based on overall water splitting

Great efforts have been made to search for highly active catalysts toward electrochemical water splitting, but double-signal immunosensors have not been reported based on bifunctional water splitting electrocatalysts. We report here a dual-signal electrochemical immunosensor for detecting carcinoembryonic antigen (CEA) using multi-wall carbon nanotubes (MWCNTs)-cobalt phosphide (CoP) as an electrocatalytic label. The preparation of MWCNTs-CoP involves the growth of Co₃O₄ nanoparticles on MWCNTs and low-temperature phosphatization of Co₃O₄ nanoparticles. The MWCNTs-CoP catalyst shows excellent electrocatalytic activities in a neutral medium toward both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), enabling MWCNTs-CoP as the electrocatalytic label for sensitive immunosensing. The linear range of the sandwich-type immunosensor for detecting CEA based on the HER signal is from 10^-4-100 ng mL^-1, whereas a linear range for detecting CEA based on the OER signal is achieved from 10^-4 to 10 ng mL^-1. The detection limits for detecting CEA using HER and OER signals are 10 and 12 fg mL^-1, respectively. This work can provide a new double-signal immunosensing platform based on a bifunctional water splitting electrocatalyst.

Gold Microstructures/Polyaniline/Reduced Graphene Oxide/Prussian Blue Composite as Stable Redox Matrix for Label-free Electrochemical Immunoassay of α-Fetoprotein

Sensitivity amplification strategies in label-free electrochemical immunosensors are mainly limited by redox molecules leaking and degradation of electrical conductivity caused by layers of decoration. Herein, a relatively stable and sensitive label-free electrochemical immunosensor based on a hierarchically flower-like gold microstructures/polyaniline/reduced graphene oxide/prussian blue (HFG/PANI/rGO/PB) composite modified electrode was stepwise fabricated for determination of α-fetoprotein (AFP). In this process, the effect of PANI and rGO on the proposed immunosensor was studied. In detail, PANI/rGO due to the unique electrochemical properties can effectively prevent PB leakage and form a stable sensing platform, which causes sensitive responsiveness and thus a more satisfied detection limit. Meanwhile, the HFG with good biological compatibility can effectively immobilize plenty of antibodies. Under optimal conditions, the HFG/PANI/rGO/PB modified immunosensor exhibited an excellent linearity (0.01 - 30 ng/mL) and a low detection limit (0.003 ng/mL) (S/N = 3), suitable specificity as well as stability and reproducibility towards AFP. The present work offered a promising platform for clinical hepatocellular carcinoma diagnostics.

Dual-Mode Electrochemical Assay of Prostate-Specific Antigen Based on Antifouling Peptides Functionalized with Electrochemical Probes and Internal References

Sensitive and selective detection of target analytes in complex biological samples is currently a major challenge. Herein we constructed a dual-mode antifouling electrochemical sensing platform for the detection of prostate-specific antigen (PSA) based on two kinds of antifouling peptides functionalized with a graphene oxide-Fe₃O₄-thionine (GO-Fe₃O₄-Thi) probe and internal reference ferrocene (Fc), respectively. The longer peptide (Pep1) modified with the GO-Fe₃O₄-Thi probe was designed to contain a peptide sequence (HSSKLQK) capable of being recognized and cut by PSA. The GO-Fe₃O₄-Thi probe functions not only as a peroxidase mimick (GO-Fe₃O₄) but also works as an electrochemical probe due to the presence of thionine (Thi). The concentration of PSA can be measured through both the increase of differential pulse voltammetry (DPV) signal change of Thi and the decrease of chronoamperometry (CA) signal of the reduction of H₂O₂ electrocatalyzed by GO-Fe₃O₄. The shorter peptide (Pep2) was tagged with Fc, whose DPV signal remained constant and was independent of the presence of PSA, and it was used as an internal reference to ensure the reliability and accuracy of the measurement. The dual-mode PSA sensor exhibits a wide linear range from 5 pg/mL to 10 ng/mL, with low detection limits of 0.76 and 0.42 pg/mL through DPV and CA modes, respectively. More importantly, owing to the antifouling capability of the designed peptides, the biosensor performances remained operable even in human serum, indicating feasibility of the electrochemical biosensor for practical PSA quantification in complex samples.