A dual-mode PCT electrochemical immunosensor with CuCo2S4 bimetallic sulfides as enhancer

Biofunctional photoelectrochemical/electrochemical immunosensor based on BiVO4/BiOI-MWCNTs and Au@PdPt for alpha-fetoprotein detection

A biofunctional immunosensor combining photoelectrochemical (PEC) and electrochemical (EC) was proposed for the quantitative detection of the liver cancer marker alpha-fetoprotein (AFP) in human blood. BiVO4/BiOI-MWCNTs photoactive materials were first prepared on conductive glass FTO, and the photoelectrode was functionalized by chitosan and glutaraldehyde. Then, the AFP capture antibody (Ab1) was successfully modified on the photoelectrode, and the label-free rapid detection of AFP antigen was achieved by PEC. In addition, Au@PdPt nanospheres were also used as a marker for binding to AFP detection antibody (Ab2). Due to the excellent catalytic properties of Au@PdPt in EC reaction, a signal increase in the EC response can be achieved when Ab2 binds to the AFP antigen, which ensures high sensitivity for the detection of AFP. The detection limits of PEC and EC are 0.050 pg/mL and 0.014 pg/mL, respectively. The sensor also possesses good specificity, stability and reproducibility, shows excellent performance in the detection of clinical samples and has good clinical applicability.

AuPt/NF prepared with the lattice induction of substrate was applied to construct the electrochemical immunosensor for PCT detection

For the electrodeposition, the conductivity and lattice structure of substrate is important to the morphology and lattice of the deposited material. In this study, gold-platinum (AuPt) nanopartical was deposited on nickel foam (NF) based on the lattice induced orientation of the Ni substrate, and the obtained AuPt/NF was applied to construct electrochemical impedimetric immunosensor for procalcitonin (PCT) detection. As a new immunosensor matrix, NF with higher electrical conductance, flexibility and specific surface area, which can improve the plasticity, sensitivity and universality of the immunoelectrode. Due to the lattice matching between Au and Ni, ultrathin AuPt nanolayer with good biocompatibility and large surface area can be modified on the NF surface, which can bind more biomolecules and amplifies the change of impedance signal. Based on the synergistic effect between AuPt and NF, PCT detection based on this electrochemical impedimetric immunosensor with a wide linear range (0.2 pg mL-1 to 20 ng mL-1) and low detection limit (0.11 pg mL-1). In addition, this impedimetric immunosensor exhibits high recovery in the PCT detection of serum samples. This work provides a new thought and method for the construction of electrochemical immunosensor.

Glycerate-assisted CoMn-sulfide with microsphere architecture confined by nanoparticles as an efficient enzyme-free sensor for amperometric measurement of glucose in serum, saliva and beverage samples

The preparation of binary metal chalcogenides with ideal architectures can effectively enhance the electrocatalytic properties of these materials, as promising glucose sensors. Herein, CoMn-S spheres were synthesized using CoMn-glycerate as the precursor, followed by a sulfidation reaction. First, glycerate spheres were prepared by solvothermal treatment of Co and Mn ions in isopropanol solvent mixed with glycerol. Then, CoMn-glycerate was solvothermally sulfidized using an ion-exchange process to prepare glycerate-assisted CoMn-S spheres with many nanoparticles on their surface which provide abundant electrocatalyst sites. The sensing outcomes revealed that glycerate-assisted CoMn-S spheres have impressive electroanalytical performance with high sensitivities of 5148 and 1928 μA mM-1 cm-2 in broad measuring ranges of 0.001-0.63 mM and 0.63-2.53 mM, quick response to glucose oxidation (2 s), and a low detection limit of (0.88 μM). Furthermore, the sensor has been successfully employed to measure glucose in human serum, saliva, and beverage samples such as fruit juice, milk, and soft drinks with satisfactory recoveries. The high electrocatalytic activity of the CoMn-S sphere sensor results from the synergy between the components and nanoparticle-assembled microspheres, which creates a high surface area, shortens the charge transfer routes, and improves the electro-conductivity. The performance characteristics of the glycerate-assisted CoMn-S spheres were compared with CoMn-hydroxide needles and CoMn-S sheets. The glycerate-derived design provides an efficient and effective strategy to construct the enzyme-free platforms with high assay capability.

A smartphone-assisted photoelectrochemical POCT method via Z-scheme CuCo2S4/Fe3O4 for simultaneously detecting co-contamination with microplastics in food and the environment

As emerging contaminants, microplastics threaten food and environmental safety. Dibutyl phthalate (DBP, released from microplastics) and benzo[a]pyrene (BaP, adsorbed on microplastics) coexisted in food and the environment, harming human health, requesting a sensitive and simultaneous testing method to monitor. To address current sensitivity, simultaneousness, and on-site portability challenges during dual targets in complex matrixes, CuCo2S4/Fe3O4 nanoflower was designed to develop a smartphone-assisted photoelectrochemical point-of-care test (PEC POCT). The carrier transfer mechanism in CuCo2S4/Fe3O4 was proven via density functional theory calculation. Under optimal conditions, the PEC POCT showed low detection limits of 0.126, and 0.132 pg/mL, wide linearity of 0.001-500, and 0.0005-50 ng/mL for DBP and BaP, respectively. The smartphone-assisted PEC POCT demonstrated satisfied recoveries (80.00%-119.63%) in real samples. Coherent results were recorded by comparing the PEC POCT to GC-MS (DBP) and HPLC (BaP). This novel method provides a practical platform for simultaneous POCT for food safety and environment monitoring.

A dual-mode label-free electrochemical immunosensor for ultrasensitive detection of procalcitonin by on-site vulcanization of dual-MOF heterostructure

Detection of procalcitonin (PCT) is crucial for the early identification of sepsis. PCT is primarily utilized in the multiple diagnosis of bacterial and viral illnesses along with to guide the application of antibiotics. Considering their advantages of high specificity and straightforward usage, electrochemical immunosensors offer significant application prospects in the detection of disease indicators. A dual-mode electrochemical immunosensor was constructed in this study to reliably identify PCT. In light of the synergistic effect of the dual-MOF derived heterostructure, the immunosensor demonstrating excellent square wave voltammetry (SWV) signals as well as significant catalytic activity for the H2O2 redox process. In addition to maintaining a low detection limit (SWV: 0.31 fg/mL and i-t: 0.098 fg/mL), the immunosensor offers an extensive linear response range (0.000001-100 ng/mL). The excellent performance is on account of the introduction of the local on-site sulfurized dual-MOF heterostructure with abundant metal chalcogenides/MOF interfaces, which boosts the specific surface area, offers an abundance of active sites, enhances conductivity, and raises catalytic activity. Furthermore, the immunosensor exhibits outstanding specificity, stability and reproducibility for the determination of PCT in serum, which is of great crucial for the clinical screening and diagnosis of sepsis.

Enhanced visible light driven photodegradation of rifampicin and Cr(VI) reduction activity of ultra-thin ZnO nanosheets/CuCo2S4QDs: A mechanistic insights, degradation pathway and toxicity assessment

In this study, we focused on fabrication of porous ultra-thin ZnO nanosheet (PUNs)/CuCo2S4 quantum dots (CCS QDs) for visible light-driven photodegradation of rifampicin (RIF) and Cr(VI) reduction. The morphology, structural, optical and textural properties of fabricated photocatalyst were critically analyzed with different analytical and spectroscopic techniques. An exceptionally high RIF degradation (99.97%) and maximum hexavalent Cr(VI) reduction (96.17%) under visible light was achieved at 10 wt% CCS QDs loaded ZnO, which is 213% and 517% greater than bare ZnO PUNs. This enhancement attributed to the improved visible light absorption, interfacial synergistic effect, and high surface-rich active sites. Extremely high generation of ●OH attributed to the spin-orbit coupling in ZnO PUNs@CCS QDs and the existence of oxygen vacancies. Besides, the ZnOPUNs@CCS QDs, forming Z-scheme heterojunctions, enhanced the separation of photogenerated charge carriers. We investigated the influencing factors such as pH, inorganic ions, catalyst dosage and drug dosage on the degradation process. More impressively, a stable performance of ZnO PUNs@CCS QDs obtained even after six consecutive degradation (85.9%) and Cr(VI) reduction (67.7%) cycles. Furthermore, the toxicity of intermediates produced during the photodegradation process were assessed using ECOSAR program. This work provides a new strategy for ZnO-based photocatalysis as a promising candidate for the treatment of various contaminants present in water bodies.

Micromotor-based dual aptassay for early cost-effective diagnosis of neonatal sepsis

Given the long-life expectancy of the newborn, research aimed at improving sepsis diagnosis and management in this population has been recognized as cost-effective, which at early stages continues to be a tremendous challenge. Despite there is not an ideal-specific biomarker, the simultaneous detection of biomarkers with different behavior during an infection such as procalcitonin (PCT) as high specificity biomarker with one of the earliest biomarkers in sepsis as interleukin-6 (IL-6) increases diagnostic performance. This is not only due to their high positive predictive value but also, since it can also help the clinician to rule out infection and thus avoid the use of antibiotics, due to their high negative predictive value. To this end, we explore a cutting-edge micromotor (MM)-based OFF-ON dual aptassay for simultaneous determination of both biomarkers in 15 min using just 2 μL of sample from low-birth-weight neonates with gestational age less than 32 weeks and birthweight below 1000 g with clinical suspicion of late-onset sepsis. The approach reached the high sensitivities demanded in the clinical scenario (LODPCT = 0.003 ng/mL, LODIL6 = 0.15 pg/mL) with excellent correlation performance (r > 0.9990, p < 0.05) of the MM-based approach with the Hospital method for both biomarkers during the analysis of diagnosed samples and reliability (Er < 6% for PCT, and Er < 4% for IL-6). The proposed approach also encompasses distinctive technical attributes in a clinical scenario since its minimal sample volume requirements and expeditious results compatible with few easy-to-obtain drops of heel stick blood samples from newborns admitted to the neonatal intensive care unit. This would enable the monitoring of both sepsis biomarkers within the initial hours after the manifestation of symptoms in high-risk neonates as a valuable tool in facilitating prompt and well-informed decisions about the initiation of antibiotic therapy.These results revealed the asset behind micromotor technology for multiplexing analysis in diagnosing neonatal sepsis, opening new avenues in low sample volume-based diagnostics.

Electrochemical immunosensor based on hollow Pt@Cu2O as a signal label for dual-mode detection of procalcitonin

As a reliable biomarker to evaluate the severity of sepsis, sensitive and accurate detection of procalcitonin (PCT) is essential. In this study, a dual-mode electrochemical immunosensor based on Au/ZIF-8 as substrate and Pt@Cu2O as signal label was constructed for the detection of PCT. By loading Au nanoparticles onto rhombic dodecahedral ZIF-8, the substrate (Au/ZIF-8) has large specific surface area and can immobilize antibody (Ab1) by Au-N bonds. Meanwhile, hollow Pt@Cu2O nanocomposite with excellent peroxidase-like activity and electrocatalytic activity were synthesized as signal label. In the process of electrochemical testing, Pt@Cu2O catalyzed the reduction of hydrogen peroxide (H2O2) and further promotes the oxidation of hydroquinone (HQ) to achieve the synergistic amplification of electrochemical signals. The proposed immunosensor detected PCT by amperometric i-t and differential pulse voltammetry (DPV) tests with a good linear response and low limit of detection (i-t: 0.70 fg/mL and DPV: 0.40 fg/mL) in the range of 10 fg/mL∼100 ng/mL. The immunosensor exhibited excellent sensitivity and accuracy, indicating the potential application of this method for PCT detection.

Dual-signal ratiometric electrochemical immunosensor constructed with snowflake-like FeSe2-AuNPs and PAA-ZIF@TB for sensitive detection of CYFRA21-1

In this study, a ratiometric electrochemical immunosensor has been developed to detect the cytokeratin 19 fragment 21-1 (CYFRA21-1) biomarker in a highly sensitive manner through a dual-signal output model. As one of signal indicators, snowflake-like FeSe₂ loaded with AuNPs (FeSe₂-AuNPs) as sensing substrate with good conductivity and large active sites provides a differential pulse voltammetry (DPV) signal at +0.4 V. Another signal indicator, toluidine blue (TB) with the water-solubility property is an excellent redox probe that can generate DPV signal at -0.3 V. To solve the water-solubility problem, the TB is absorbed with polyacrylic acid (PAA) functionalized ZIF-67 (PAA-ZIF-67), which retains the properties of ZIF-67 that are large specific surface area and strong adsorption properties. The ratio of signals, stemmed from PAA-ZIF@TB and FeSe₂-AuNPs (I_PAA-ZIF@TB/I_FeSe2-AuNPs), increases with the CYFRA21-1 concentration. Under optimal experimental conditions, CYFRA21-1 was detected in a wide dynamic range from 0.1 pg/mL to 100 ng/mL, with a lower limit of detection of 0.02 pg/mL. Looking ahead, this ratio based strategy provides prospective clinical applications for detecting other biomarkers.

The Applications of Electrochemical Immunosensors in the Detection of Disease Biomarkers: A Review

Disease-related biomarkers may serve as indicators of human disease. The clinical diagnosis of diseases may largely benefit from timely and accurate detection of biomarkers, which has been the subject of extensive investigations. Due to the specificity of antibody and antigen recognition, electrochemical immunosensors can accurately detect multiple disease biomarkers, including proteins, antigens, and enzymes. This review deals with the fundamentals and types of electrochemical immunosensors. The electrochemical immunosensors are developed using three different catalysts: redox couples, typical biological enzymes, and nanomimetic enzymes. This review also focuses on the applications of those immunosensors in the detection of cancer, Alzheimer's disease, novel coronavirus pneumonia and other diseases. Finally, the future trends in electrochemical immunosensors are addressed in terms of achieving lower detection limits, improving electrode modification capabilities and developing composite functional materials.

Ultrasensitive Photoelectrochemical Immunoassay Strategy Based on Bi2S3/Ag2S for the Detection of the Inflammation Marker Procalcitonin

As an inflammatory marker, procalcitonin (PCT) is more representative than other traditional inflammatory markers. In this work, a highly efficient photoelectrochemical (PEC) immunosensor was constructed based on the photoactive material Bi₂S₃/Ag₂S to realize the sensitive detection of PCT. Bi₂S₃ was prepared by a hydrothermal method, and Ag₂S quantum dots were deposited on the ITO/Bi₂S₃ surface via in situ reduction. Bi₂S₃ is a kind of admirable photoelectric semiconductor nanomaterial on account of its moderate bandgap width and low binding rate of photogenerated electron holes, which can effectively convert light energy into electrical energy. Therefore, based on the energy level matching principle of Bi₂S₃ and Ag₂S, a labeled Bi₂S₃/Ag₂S PEC immunosensor was constructed, and the sensitive detection of PCT was successfully established. The linear detection range of the PEC immunosensor was 0.50 pg∙mL^-1 to 50 ng∙mL^-1, and the minimum detection limit was 0.18 pg∙mL^-1. Compared with the traditional PEC strategy, the proposed PEC immunosensor is simple, convenient, and has good anti-interference, sensitivity, and specificity, which could provide a meaningful theoretical basis and reference value for the clinical detection of PCT.

Detection of COVID-19-related biomarkers by electrochemical biosensors and potential for diagnosis, prognosis, and prediction of the course of the disease in the context of personalized medicine

As a more efficient and effective way to address disease diagnosis and intervention, cutting-edge technologies, devices, therapeutic approaches, and practices have emerged within the personalized medicine concept depending on the particular patient's biology and the molecular basis of the disease. Personalized medicine is expected to play a pivotal role in assessing disease risk or predicting response to treatment, understanding a person's health status, and, therefore, health care decision-making. This work discusses electrochemical biosensors for monitoring multiparametric biomarkers at different molecular levels and their potential to elucidate the health status of an individual in a personalized manner. In particular, and as an illustration, we discuss several aspects of the infection produced by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) as a current health care concern worldwide. This includes SARS-CoV-2 structure, mechanism of infection, biomarkers, and electrochemical biosensors most commonly explored for diagnostics, prognostics, and potentially assessing the risk of complications in patients in the context of personalized medicine. Finally, some concluding remarks and perspectives hint at the use of electrochemical biosensors in the frame of other cutting-edge converging/emerging technologies toward the inauguration of a new paradigm of personalized medicine.

Smartphone-based microplate reader for high-throughput quantitation of disease markers in serum

Herein, a smartphone-based portable reader with integrated optics for standard microtiter plates (96 wells) has been designed and demonstrated for high-throughput quantitation of validated biomarkers in serum. The customized optical attachment was simply constructed with a convex lens and a light source, by which the transmitted light through a 96-well microtiter plate was converged for imaging with a smartphone, so that accurate and wide-range reading of the plate can be achieved. More importantly, relying on the digitized colorimetric analysis of the obtained images, concentrations of various biomarkers can be determined directly using the customized mobile app. A set of validated biomarkers for inflammation and infection, C-reactive protein (CRP), serum amyloid A (SAA), and procalcitonin (PCT) have been quantitated with this new system; both the response ranges and limits of detection meet the requirement of clinical tests. The consistency with the results obtained using a commercial microplate reader proves its reliability and precision, augments its potential as a point-of-care diagnostic device for on-site testing or resource-limited settings.

Diagnostic value of procalcitonin, hypersensitive C-reactive protein and neutrophil-to-lymphocyte ratio for bloodstream infections in pediatric tumor patients

OBJECTIVES

Bloodstream infection (BSI) is one of the major causes of death in pediatric tumor patients. Blood samples are relatively easy to obtain and thus provide a ready source of infection-related biological markers for the prompt evaluation of infection risk.

METHODS

A total of 259 pediatric tumor patients were included from May 2019 to March 2022. Patients were divided into BSI group (n=70) and control group (n=189). Clinical and biological data were collected using electronic medical records. Differences in biological markers between BSI group and control group and differences before and during infection in BSI group were analyzed.

RESULTS

The infected group showed higher levels of procalcitonin (PCT) and hypersensitive C-reactive-protein (hsCRP), and lower prealbumin (PA) than the uninfected group. Area under the receiver-operating curve (ROC) curves (AUC) of PCT, hsCRP and NLR (absolute neutrophil count to the absolute lymphocyte count) were 0.756, 0.617 and 0.612. The AUC of other biomarkers was ≤0.6. In addition, PCT, hsCRP, NLR and fibrinogen (Fg) were significantly increased during infection, while PA and lymphocyte (LYM) were significantly decreased. Antibiotic resistant of Gram-positive bacteria to CHL, SXT, OXA and PEN was lower than that of Coagulase-negative Staphylococcus. Resistant of Gram-positive bacteria to CHL was lower, while to SXT was higher than that of Gram-negative bacteria.

CONCLUSIONS

This study explored the utility of biomarkers to assist in diagnosis and found that the PCT had the greatest predictive value for infection in pediatric tumor patients with BSI. Additionally, the PCT, hsCRP, NLR, PA, LYM and Fg were changed by BSI.

CoNi-RGO and NiCo2S4-ZIF/g-C3N4 signal amplified electrochemical immunosensors for sensitive detection of CYFRA 21-1

Herein, a signal amplified electrochemical immunosensor for the sensitive detection of cytokeratin 19 fragments (CYFRA 21-1) in human serum was discussed. The CoNi-RGO was used as a substrate for the sensor with excellent specific surface area and strong electrical conductivity, which enables more efficient attachment of antibodies. The introduction of the bimetallic sulfide NiCo₂S₄ composite ZIF material provides strong catalytic performance for the immunosensor. It is worth noting that, in addition to these satisfactory advantages, these two materials also show amazing signal amplification capacity. When the immunosensor works, the increase in electrical impedance decreases the electron transfer rate, making the electrochemical signal change obvious. The signal enhancement of immunosensors was emphasized by the marker during construction, and the experimental results were satisfactory. The proposed signal enhanced immunosensor had a linear relationship in the range of 0.001-10 ng/mL for CYFRA 21-1, and the minimum detection limit was 0.33 pg/mL for △I = 95.22 + 23.27 lg c. This demonstrates that the electrochemical immunosensor we constructed is successful and has a great developing potential.

Preparation of a pH-responsive controlled-release electrochemical immunosensor based on polydopamine encapsulation for ultrasensitive detection of alpha-fetoprotein

To accomplish ultra-sensitive detection of alpha-fetoprotein(AFP), a novel electrochemical immunosensor using polydopamine-coated Fe₃O₄ nanoparticles (PDA@Fe₃O₄ NPs) as a smart label and polyaniline (PANI) and Au NPs as substrate materials has been created. The sensor has the following advantages over typical immunoassay technology: (1) The pH reaction causes PDA@Fe₃O₄ NPs to release Prussian blue (PB) prosoma while also destroying the secondary antibody label and immunological platform and lowering electrode impedance; (2) PB has a highly efficient catalytic effect on H₂O₂, allowing for the obvious amplification of electrical impulses; (3) PANI was electrodeposited on the electrode surface to avoid PB loss and signal leakage, which effectively absorbed and fixed PB while considerably increasing electron transmission efficiency. The sensor's detection limit was 0.254 pg·mL^-1 (S/N = 3), with a detection range of 1 pg·mL^-1 to 100 ng·mL^-1. The sensor has a high level of selectivity, repeatability, and stability, and it is predicted to be utilized to detect AFP in real-world samples.

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.

Micro- and nanosensors for detecting blood pathogens and biomarkers at different points of sepsis care

Severe infections can cause a dysregulated response leading to organ dysfunction known as sepsis. Sepsis can be lethal if not identified and treated right away. This requires measuring biomarkers and pathogens rapidly at the different points where sepsis care is provided. Current commercial approaches for sepsis diagnosis are not fast, sensitive, and/or specific enough for meeting this medical challenge. In this article, we review recent advances in the development of diagnostic tools for sepsis management based on micro- and nanostructured materials. We start with a brief introduction to the most popular biomarkers for sepsis diagnosis (lactate, procalcitonin, cytokines, C-reactive protein, and other emerging protein and non-protein biomarkers including miRNAs and cell-based assays) and methods for detecting bacteremia. We then highlight the role of nano- and microstructured materials in developing biosensors for detecting them taking into consideration the particular needs of every point of sepsis care (e.g., ultrafast detection of multiple protein biomarkers for diagnosing in triage, emergency room, ward, and intensive care unit; quantitative detection to de-escalate treatment; ultrasensitive and culture-independent detection of blood pathogens for personalized antimicrobial therapies; robust, portable, and web-connected biomarker tests outside the hospital). We conclude with an overview of the most utilized nano- and microstructured materials used thus far for solving issues related to sepsis diagnosis and point to new challenges for future development.

Carbon-Based Nanocomposite Smart Sensors for the Rapid Detection of Mycotoxins

Carbon-based nanomaterials have become the subject of intensive interest because their intriguing physical and chemical properties are different from those of their bulk counterparts, leading to novel applications in smart sensors. Mycotoxins are secondary metabolites with different structures and toxic effects produced by fungi. Mycotoxins have low molecular weights and highly diverse molecular structures, which can induce a spectrum of biological effects in humans and animals even at low concentrations. A tremendous amount of biosensor platforms based on various carbon nanocomposites have been developed for the determination of mycotoxins. Therefore, the contents of this review are based on a balanced combination of our own studies and selected research studies performed by academic groups worldwide. We first address the vital preparation methods of biorecognition unit (antibodies, aptamers, molecularly imprinted polymers)-functionalized carbon-based nanomaterials for sensing mycotoxins. Then, we summarize various types of smart sensors for the detection of mycotoxins. We expect future research on smart sensors to show a significant impact on the detection of mycotoxins in food products.

Recent Progress in Electrochemical Immunosensors

Biosensors used for medical diagnosis work by analyzing physiological fluids. Antibodies have been frequently used as molecular recognition molecules for the specific binding of target analytes from complex biological solutions. Electrochemistry has been introduced for the measurement of quantitative signals from transducer-bound analytes for many reasons, including good sensitivity. Recently, numerous electrochemical immunosensors have been developed and various strategies have been proposed to detect biomarkers. In this paper, the recent progress in electrochemical immunosensors is reviewed. In particular, we focused on the immobilization methods using antibodies for voltammetric, amperometric, impedimetric, and electrochemiluminescent immunosensors.

Ti3C2 MXene anchors CuAu-LDH multifunctional two-dimensional nanomaterials for dual-mode detection of CEA in electrochemical immunosensors

Electrochemical immunoassays are commonly used to detect biomarkers and Ti₃C₂ MXene anchored CuAu-LDH two-dimensional hydroxide heterojunctions for dual-mode electrochemical immunosensors were fabricated in this work. Layered double hydroxides have a large surface area, high chemical stability, tunable metal composition and interchangeable anions, however, the insulating nature of LDH further limits its catalytic performance. For this reason, Ti₃C₂ Mxenes were introduced to improve this problem. 2D layers of Ti₃C₂ Mxenes with large specific surface area and excellent conductivity have been well proven and widely used. And the surface of Ti₃C₂ Mxenes (due to the presence of abundant surface functional groups), will facilitate the anchoring of metal ions and the nucleation of LDH. In addition, its excellent electrical conductivity will facilitate the electron transfer between Cu²⁺ and Cu⁺. The immunosensor not only showed a heavy square wave voltammetry (SWV) signal. It also exhibited high electrocatalytic activity for H₂O₂ redox reactions and improves the sensitivity of the Ampere Current (i-t) detection. The CEA immunosensor developed in this study showed a wide linear response (0.0001-80 ng/mL) and the lowest detection limits (SWV: 33.6 fg/mL and i-t: 45.4 fg/mL S/N = 3). The results confirmed the excellent analytical capability of the immunosensor.

Split-Type Electrochemical Immunoassay System Triggering Ascorbic Acid-Mediated Signal Magnification Based on a Controlled-Release Strategy

This research put forward a novel split-type electrochemical (EC) immunosensor which integrated the controlled-release strategy with EC detection for application in the field of biosensing. Concretely, ascorbic acid (AA) was packaged in a cadmium sulfide (CdS)-capped spherical mesoporous bioactive glass (SBG) nanocarrier (SBG_CdS) on account of encapsulation technology. To reduce the complexity of the bioanalysis, the detection antibody-labeled SBG_CdS-AA bioconjugate was applied in a 96-well microplate for the immunoreaction process, which is independent of the EC determination procedure. Thus, the immune interference and steric hindrance caused by the accumulation of nanomaterials on the electrode could be minimized. Subsequently, AA was released efficiently via the destruction effect of dithiothreitol on the disulfide bond. In addition, for the as-prepared FcAI/l-Cys/gold nanoparticles (GNPs)/porous BiVO₄ (p-BVO)/ITO EC sensing platform in the detection solution, the synergetic catalysis of Fc and GNPs/p-BVO toward the oxidation of the released AA could be realized, which triggered AA-mediated significant signal magnification throughout this study. In particular, p-BVO with an ordered nanoarray structure could accelerate the electron transfer to assist in sensitivity improvement of this system. This novel biosensor was capable of assaying the neuron-specific enolase (NSE) biomarker sensitively, from which a linear range of 0.001-100 ng/mL was derived along with a low detection limit of 1.08 pg/mL. An innovative way could be paved in the bioanalysis of NSE and other biomarkers.

The establishment of an immunosensor for the detection of SPOP

In this paper, we first synthesis three-dimensional jasmine-like Cu@L-aspartic acid(L-ASP) inorganic–organic hybrid nanoflowers to load palladium-platinum nanoparticles (Pd–Pt NPs) as the signal enhancer in order to quantify intracellular speckle-type POZ domain protein. Scanning electron microscope, fourier transform infrared, energy dispersive spectrometer, X-ray photoelectron spectroscopy analysis was used to characterize the newly synthesized materials. The newly formed Cu@L-Asp/Pd-PtNPs can catalyze the decomposition of hydrogen peroxide and exhibit excellent catalytic performance. When different concentration of speckle-type POZ domain protein is captured by speckle-type POZ domain protein antibody linked to the surface of Cu@L-Asp/Pd–Pt NPs, the current signal decreases with the increase concentration of speckle-type POZ domain protein. After optimization, the speckle-type POZ domain protein immunosensor exhibited a good linear response over a concentration range from 0.1–1 ng mL⁻¹ with a low detection limit of 19 fg mL⁻¹. The proposed sensor demonstrates good stability within 28 days, acceptable reproducibility (RSD = 0.52%) and selectivity to the speckle-type POZ domain protein in the presence of possible interfering substances and has potential application for detecting other intracellular macromolecular substances.

Ultrasensitive near-infrared electrochemiluminescence biosensor derived from Eu-MOF with antenna effect and high efficiency catalysis of specific CoS2 hollow triple shelled nanoboxes for procalcitonin

In this paper, we report a novel multiple amplification strategy for ultrasensitive near-infrared electrochemiluminescence (ECL) immunoassay in K₂S₂O₈ solution. The realization of this strategy is based on the antenna effect of Eu-MOF (EuBTC) and a high efficiency catalysis of CoS₂ hollow triple shelled nanoboxes (TSNBs). The H₃BTC ligand in the antenna effect first undergoes π-π* absorption and a singlet-singlet electronic transition. Its energy passes through the intersystem to the triplet state, next transfers from the lowest excited triplet state to the vibrational energy level of the rare earth ion, finally realizing sensitizing center ion luminescence. Moreover, ionic reaction and structural advantages endow CoS₂ TSNBs a dual signal enhancement effect. This sandwich-type ECL biosensor has a near-infrared luminescence in 800-900 nm, thus avoiding damage to the sample in the meantime. In practical diagnosis, the normal critical value of procalcitonin (PCT) (<0.5 ng/mL) is much higher than the detection limit (3.65 fg/mL) and is in the detection range (10 fg/mL-100 ng/mL), which means that the ECL biosensor has a high sensitivity in the detection of PCT and meet the requirement for diagnosis of disease completely. Therefore, the strategy provides a feasible method for efficient and stable analysis of systemic inflammatory response such as fearful bacterial infection, hepatitis B, and peritonitis.

A dual-mode label-free electrochemical immunosensor for ultrasensitive detection of procalcitonin based on g-C3N4-NiCo2S4-CNTs-Ag NPs

Herein, a label-free electrochemical immunosensor based on differential pulse voltammetry (DPV) and amperometric i-t curve (i-t) dual-mode analysis is proposed for early quantitative detection of procalcitonin (PCT). Due to the advantages of high chemical stability and biocompatibility, graphite carbon nitride (g-C₃N₄) was adopted as a high-capacity sensing interface to carry signal indicators. As an effective indicator of chronoamperometry, nickel cobalt sulfide (NiCo₂S₄) was uniformly dispersed on the surface of g-C₃N₄ through in-situ hydrothermal synthesis, which not only promotes the activation of bimetallic activity, but also effectively prevents the aggregation of NiCo₂S₄. At the same time, in order to establish a dual-mode analysis platform to improve accuracy and sensitivity, highly conductive carbon nanotubes (CNTs) were hybridized with composite materials to load Ag nanoparticles (Ag NPs), which have excellent oxidizing properties and are used as indicators of DPV. On account of this advanced sensing strategy, a wide linear response (DPV: 0.05 ng mL^-1-50 ng mL^-1 and i-t: 1.00 pg mL^-1-10.00 ng mL^-1) and a low detection limit (DPV: 16.70 pg mL^-1 and i-t: 0.33 pg mL^-1) are demonstrated. The immunosensor synthesized by this method has good stability and sensitivity, which could be applied in clinical diagnosis and treatment.

A label-free electrochemical immunosensor based on encapsulated signal molecules in mesoporous silica-coated gold nanorods for ultrasensitive assay of procalcitonin

For immobilization and signal amplification of the probes, it is feasible and promising by using porous nanomaterials as nanocarriers. Herein, a novel label-free electrochemical immmunosensor was efficiently designed for ultrasensitive detection of procalcitonin (PCT). The immunosensor was prepared by using porous silica-coated gold nanorods (Au NRs@m-SiO₂) to load electroactive dye thionine (Thi) on the electrode surface. Apart from the improved electrical conductivity, the porous feature highly increased the loading amount of Thi to boost the detection signals, while the good biocompatibility and protective microenvironment are beneficial to the largely improved stability for the target. For quantification of PCT, the developed immunosensor exhibited a good linear relationship in the antigen concentration range of 0.001-100 ng mL^-1 with an ultra-low limit of detection (LOD, 0.39 pg mL^-1, S/N = 3). Moreover, the built platform was successfully applied to such assay in human serum samples. The research provides some valuable guidelines for clinical screening and diagnosis of other biomarkers.

Dual-Signaling Electrochemical Ratiometric Method for Competitive Immunoassay of CYFRA21-1 Based on Urchin-like Fe3O4@PDA-Ag and Ni3Si2O5(OH)4-Au Absorbed Methylene Blue Nanotubes

A novel ratiometric electrochemical (EC) sensing platform was established for sensitive immunoassay of target cytokeratin 19 fragment 21-1 (CYFRA21-1) biomarker by combining competitive immunoreaction and multisignal output. This immunosensor utilized Ag nanoparticles (NPs)-functionalized urchin-like Fe₃O₄@polydopamine (u-Fe₃O₄@PDA-Ag) as a matrix to immobilize CYFRA21-1 antigens and methylene blue (MB)-absorbed Ni₃Si₂O₅(OH)₄-Au nanotubes (NTs) to label the anti-CYFRA21-1 (Ab). During the competitive immunoreaction, square wave voltammetric (SWV) current changes of Ag NPs from u-Fe₃O₄@PDA-Ag indicator and MB from Ni₃Si₂O₅(OH)₄-Au/MB indicator are relevant to the dosage of CYFRA21-1-acquired Ni₃Si₂O₅(OH)₄-Au/MB/Ab. More importantly, numerous CYFRA21-1 loaded stably on u-Fe₃O₄@PDA-Ag exhibited strong competitive capacity toward the target-CYFRA21-1 to combine Ni₃Si₂O₅(OH)₄-Au/MB/Ab, causing sensitive changes in the ratio of two measured SWV currents. Prominently, "ΔI = ΔI_MB + |ΔI_Ag NPs|" (ΔI_MB and |ΔI_Ag NPs| represents the change values of the oxidation peak currents of MB and Ag NPs, respectively) could be regarded as significantly amplifying the signal response and ultimately improving the sensitivity of CYFRA21-1 detection, from which we derived a wide dynamic range from 500 fg/mL to 50 ng/mL and a low detection limit of 0.39 pg/mL (S/N = 3). This work may exert a profound impact on monitoring other biomarkers in early diagnosis of diseases.

Enzyme-induced Cu2+/Cu+ conversion as the electrochemical signal for sensitive detection of ethyl carbamate

Traditional enzyme-linked immunosorbent assay (t-ELISA) method suffers from its relatively low sensitivity or accuracy in the detection of trace level of analyte in complicated samples. In this work, to extend the application of ELISA in practical samples, a newly electrochemical immunoassay (ECIA) was developed based on an enzyme-induced Cu²⁺/Cu⁺ conversion for the determination of ethyl carbamate (EC). Wherein, three rounds of signal transformation-the catalysis of ALP enzyme, the conversion of Cu²⁺/Cu⁺ and signal output of square wave voltammetry (SWV), can be realized to obtain higher sensitivity as compared to t-ELISA. The ECIA method combines the advantages of electrochemistry and ELISA, behaving superior detection performance, such as good selectivity, high sensitivity, and low background signal. For the wine samples, the method showed a linear detection range from 2.5 nM to 2.5 × 10⁴ nM with a limit of detection of 2.28 nM (S/N = 3), which reveals that the ECIA sensor is a promising platform for the detection of trace level of EC in practical samples.