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

Homogeneous electrochemical ratiometric biosensor for MircoRNA detection based on UiO-66-NH2 signal probe and waste-free entropy-driven DNA machine

The construction of efficient methods for highly sensitive and rapid detection of disease markers is essential for the early diagnosis of serious diseases. In this paper, taking advantage of the UiO-66-NH2 signal molecule in combination with a waste-free entropy-driven DNA machine, a novel homogeneous electrochemical ratiometric platform is developed to detect MircoRNA (miRNA). Metal-organic framework materials (UiO-66-NH2 MOF) and ferrocene were utilized as electrochemical signal tags and reference probes, respectively. The target-initiated waste-free three-dimensional (3D) entropy-driven DNA nanomachine is activated in the presence of miRNA, resulting in DNA-labeled-UiO-66-NH2 falling off from the electrode, leading to a decrease in the signal of UiO-66-NH2 at 0.83V. Our strategy can mitigate false positive responses induced by the DNA probes immobilized on electrodes in traditional distance-dependent signal adjustment ratiometric strategies. The proposed ratiometric platform demonstrates superior sensitivity (a detection limit of 9.8 fM), simplified operation, high selectivity, and high repeatability. The ratiometric biosensor is also applied to detect miRNA content in spiked serum samples.

Magnetic copper silicate and boronic acid-conjugated AuNCs@keratin-based electrochemical/fluorescent dual-sensing for carcinoembryonic antigen

Boronic Acid Sensitivity, selectivity, and reliability are of great importance for tumor diagnosis. Herein, we proposed a novel electrochemical and fluorescent dual-sensing strategy to detect carcinoembryonic antigens (CEA). To this end, monodisperse spindle-like magnetic copper silicate (FeOx@C@CS) was prepared with multiple active sites to immobilize the CEA antibody. Moreover, magnetic properties improved the anti-interference ability and sensitivity to endow the assay for complex samples. In addition, boronic acid-conjugated gold nanocluster (AuNCs@keratin-BA) was prepared as an electrochemical and fluorescent dual-signal indicator. Thus, the sandwich structure of FeOx@C@CS/CEA/AuNCs@keratin-BA was formed for electrochemical/fluorescent dual-modality assay. Under optimal conditions, the quantitation range of 12.5 fg mL-1-37.5 pg mL-1 and detection limit of 4.3 fg mL-1 were obtained for the electrochemical strategy. The fluorescence detection owned the linear range of 0.05 pg mL-1-7.5 pg mL-1 with a detection limit of 0.025 pg mL-1. Dual-modality assay improved the accuracy and efficiency of CEA detection to meet the requirement of tumor diagnosis, while chemical identification and signal transduction lay an important foundation for engineering advanced nanomaterials for clinical applications.

Silver nanoparticles in electrochemical immunosensing and the emergence of silver-gold galvanic exchange detection

Nanoparticle-based electrochemical immunosensors demonstrate high sensitivity toward biomarker detection due to the large surface area of the nanoparticles and their ability to amplify the signal of the target molecule. Additionally, they have a fast response time, relatively lower cost, and can be easily miniaturized for point-of-care applications. Among noble metals, silver nanoparticles (AgNPs) have been extensively used in electrochemical sensors due to their unique properties, such as catalytic activity and excellent electrical conductivity. This Feature Article describes six approaches for incorporating AgNPs in electrochemical platforms, featuring the most recent developments in the silver-gold galvanic exchange-based detection strategy. With a few exceptions, many of these detection methods use AgNP oxidation into Ag+ ions, followed by electrodeposition of Ag+ ions onto the working electrode as zero-valent Ag metal and a final stripping step using a voltammetric technique. Combining these steps provides desirable low detection limits and good sensitivity for various biomarkers. A few other methods involved the reduction of Ag+ ions and depositing them as Ag metal onto the electrode using a reagent mixture so that the striping analysis could be performed. Typically, this reagent mixture includes Ag+ ions, a reducing agent, or an enzyme substrate. Besides, AgNPs have also been directly used to modify the surface of electrodes to facilitate kinetically favored redox-mediated electrochemical reactions. In addition to Ag detection methods, this report will also provide recent examples to illustrate how the size and shape of AgNPs impact the detection limits and sensitivity of an electrochemical assay. Finally, we discuss recent developments in lab-on-a-chip type immunosensors designed explicitly for Ag-based metalloimmunoassay detection, and we envision that this article will provide a comprehensive summary of the operational principles and new insights into such immunoassay systems.

Ratiometric Sensing for Ultratrace Tetracycline Using Electrochemically Active Metal-Organic Frameworks as Response Signals

A novel ratiometric sensor using an electrochemically active metal-organic framework of Mo@MOF-808 and NH₂-UiO-66 as response signals was developed to detect tetracycline (TET) in ultratrace quantities. To achieve the dual-response strategy, Mo@MOF-808, with a reduction peak at -1.06 V, and NH₂-UiO-66, with an oxidation peak at 0.724 V, were used as signal probes directly. Concretely, Mo@MOF-808, single-stranded DNA (ssDNA), and complex system (Apt@NH₂-UiO-66) of aptamer (Apt) and NH₂-UiO-66 were sequentially immobilized on the electrode. With the addition of TET, Apt was hybridized with TET and Apt@NH₂-UiO-66 was detached from the electrode, resulting in an increase in the current at -1.06 V and a decrease in the current at 0.724 V. Through this strategy, the sensor achieved a wide linear range (0.1-10000 nM) and a low limit of detection (0.009792 nM) for TET. Moreover, the ratiometric sensor exhibited better sensitivity, reproducibility, and stability than a single-signal sensor. Furthermore, the constructed sensor was successfully applied to detect TET in milk samples, suggesting excellent application prospects.

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.

Dual-Mode Electrochemical Competitive Immunosensor Based on Cd2+/Au/Polydopamine/Ti3C2 Composite and Copper-Based Metal-Organic Framework for 17β-Estradiol Detection

Herein, a dual-mode electrochemical competitive immunosensor was constructed for the detection of 17β-estradiol (E2) based on differential pulse voltammetry (DPV) and chronoamperometry (i-t). During the immune recognition process, the E2 antibody (E2-Ab) was immobilized on the Cd²⁺/Au/polydopamine/Ti₃C₂ (Cd²⁺/Au/pDA/Ti₃C₂) composite-modified electrode; then, the E2-conjugated bovine serum albumin (E2-BSA) was labeled with a copper-based metal-organic framework (Cu-MOF) and competed with E2 in combining the E2-Ab. The Cu-MOF was not only an electroactive species but also possessed good electrocatalytic activity toward H₂O₂. Thus, E2 could be quantified according to the peak current change of the Cu-MOF in DPV curve or the variation of H₂O₂ reduction current. For DPV quantification, Cd²⁺ was introduced as an internal reference in this case, and a highly reproducible ratio readout was obtained. The as-prepared dual-mode E2 electrochemical immunosensor showed good linear relationship in the ranges of 1 pg mL^-1-10 ng mL^-1 (DPV) and 10 pg mL^-1-10 ng mL^-1 (i-t), and the detection limits were 0.47 and 5.4 pg mL^-1 (S/N = 3), respectively. Furthermore, the dual-mode electrochemical immunosensor exhibited good practicability in real sample analysis.

Simple synthesis of PtRu nanoassemblies as signal amplifiers for electrochemical immunoassay of carbohydrate antigen 19-9

In clinical analysis, carbohydrate antigen 19-9 (CA199) is a gold standard for pancreatic cancer diagnosis. Herein, PtRu nanoassemblies (NAs) were synthesized via a facile one-step solvothermal approach, with the help of octylphenoxypolye thoxyethanol (NP-40) acted as a growth-directing molecule, and triethylene glycol (TEG) worked as a reductant and solvent. During the assembly process of small particles, a large number of voids were formed, which significantly increase the specific surface area of the PtRu NAs exhibiting excellent electrocatalytic performance. Incorporating the PtRu NAs as signal amplifiers for potassium ferrocyanide oxidation into the specific molecular recognition of proteins, a facile signal-enhanced electrochemical (EC) immunosensor was developed. Verified by a series of experiments, the proposed immunosensor presented a wide linear range (10^-4-70 U mL^-1) and a low detection limit (3.3 × 10^-5 U mL^-1), accompanied by good reproducibility, selectivity, and stability, which could be applied in human serum samples for the determination of CA199, and was comparable to commercial electrochemiluminescence (ECL) immunoassay. Feasibility of batch fabrication of PtRu NAs makes nanomaterial-based EC immunoassay promising for the determination of similar cancer markers in future.

Ultrasensitive dual-signal electrochemical ratiometric aptasensor based on Co-MOFs with intrinsic self-calibration property for Mucin 1

The concentration of tumor biomarker Mucin 1 (MUC 1) is highly related with many diseases, which can be employed for the early diagnosis of cancer. In this paper, an electrochemical ratiometric aptasensor with intrinsic self-calibration property for the detection of MUC 1 is presented. In this paper, Co-MOFs themselves were employed as signal substances. This strategy was fabricated by using gold nanoparticles@black phosphorus (BP) as the substrate on the electrode, followed by modification of DNA nanotetrahedrons (DTN) via Au-S bond. The terminal of DTN contains MUC 1 aptamer. In the presence of MUC 1, the signal of DNA-labeled Co-MOFs can be detected. The current signal of Co-MOFs increased and that of thionine (as reference) was unchanged upon the addition of MUC 1. Thus, an intrinsic self-calibration aptasensor was achieved. In order to simplify the modification procedure, the electrolyte solution thionine was employed as an inner reference probe. Moreover, coupling of the hybridization chain reaction (HCR) with these MOFs signal tags presents an enzyme-free method for signal amplification, endowing the proposed ratiometric biosensor detection with high reproducibility and high sensitivity. The current ratio (I_IR/I_SP) remained stable over 30 individual measurements performed on ten different working electrodes. Even ten repeated scans performed on a single electrode exhibited a constant current ratio. The electrochemical ratiometric aptasensor is highly sensitivity for MUC 1 with the detection limit of 1.34 fM. Our proposed ratiometric sensor has great potential for the detection of cancer-related biomarkers.

Antigen-Down PEC Immunosensor for CYFRA21-1 Detection Based on Photocurrent Polarity Switching Strategy

In this work, an antigen-down photoelectrochemical (PEC) immunosensor based on a signal polarity switching strategy for the detection of cytokeratin 19 fragment 21-1 (CYFRA21-1) was proposed. 3,4,9,10-Perylene tetracarboxylic acid (PTCA) is a conjugated organic dye containing five benzene nuclei, which has excellent film-forming and optical properties. PTCA sensitized by SnS₂ can further improve the basal signal and the stability of the PEC immunosensor. Moreover, avidin-functionalized CuInS₂ as a signal probe can convert the basal anodic photocurrent to a cathodic photocurrent. Therefore, the PEC sensor realized the photocurrent polarity conversion before and after labeling. With avidin-functionalized CuInS₂, the polarity of the photocurrent was changed once CYFRA21-1 was detected. Therefore, the PEC immunosensor owns high sensitivity. The linear range of the immunosensor for the detection of CYFRA21-1 is 0.00001-500 ng·mL^-1, and the detection limit is 3.5 fg·mL^-1. The PEC immunosensor has good stability, high selectivity, and good repeatability. This work may provide a new way for the detection of CYFRA21-1 and other proteins.

A sandwich-type electrochemical immunosensor for CYFRA 21-1 based on probe-confined in PtPd/polydopamine/hollow carbon spheres coupled with dendritic Au@Rh nanocrystals

A signal-on sandwich-like electrochemical immunosensor was built for determination of cytokeratin 19 fragments 21-1 (CYFRA 21-1) in non-small cell lung cancer (NSCLC) by confining electroactive dye (e.g., methylene blue, MB) as a probe for amplifying signals. Specifically, core-shell gold@rhodium dendritic nanocrystals (Au@Rh DNCs) behaved as a substrate for primary antibody and accelerate interfacial electron transfer. Besides, hollow carbon spheres (HCSs) were subsequently modified with polydopamine (PDA) and PtPd nanoparticles for sequential integration of the secondary antibody and confinement of MB as a label, termed as MB/PtPd/PDA/HCSs for clarity. The built sensors showed a broad linear range (100 fg mL^-1 ~ 100 ng mL^-1) for detection of CYFRA 21-1 with an ultra-low detection limit (31.72 fg mL^-1, S/N = 3), coupled with satisfactory performance in human serum samples. This work can be explored for assays of other proteins and provides some constructive insights for early and accurate diagnosis of NSCLC.

An ultrasensitive immunosensor based on cellulose nanofibrils/polydopamine/Cu-Ag nanocomposite for the detection of AFP

In this work, an ultrasensitive immunosensor for amperometric determination of alpha-fetoprotein (AFP) was developed utilizing Ag and Cu nanoparticles on polydopamine (PDA) functionalized cellulose nanofibrils (CNFs) composite (CNFs/PDA/Cu-Ag) as signal amplifier. PDA was first prepared by self-polymerizing of dopamine, and then was adsorbed on CNFs. The obtained CNFs/PDA was applied as substrate to electrolessly deposit Cu-Ag nanoparticles, using NaBH₄ as reducing agent. The structure and morphology of the synthesized CNFs/PDA/Cu-Ag nanocomposite were analyzed through Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray powder diffraction, scanning electron microscopy, particle size analyzer and transmission electron microscopy. The CNFs/PDA/Cu-Ag modified glassy carbon electrode can fix AFP antibody (Ab), and further capture AFP specifically. Electrochemical impedance spectroscopy and cyclic voltammetry were used to characterize the assembly process of immunosensor. The immunoreaction was amplified by electrocatalytical reduction of H₂O₂ on Cu-Ag nanoparticles, through which AFP was quantitatively detected. The developed sensor exhibits wide linear range of 0.01-100 ng mL^-1 (R² = 0.9963) with low detection limit of 4.27 pg mL^-1 (S/N = 3). In addition, it has been used for the detection of AFP in human serum, manifesting its preeminent application prospect in early liver cancer diagnosis.

Designing Triangular Silver Nanoplates with GSH/GSSG Surface Mixed States as Novel Nanoparticle-based Redox Mediators for Electrochemical Biosensing

Herein, a dual signal-quenched electrochemical (EC) biosensing strategy utilizing surface-engineered trisodium citrate (TSC)-glutathione (GSH)/oxidized glutathione (GSSG)-capped triangular silver nanoplates (Tri-Ag NPs_TSC-GSH/GSSG) as a novel nanoparticle-based redox mediator was explored for biomarker determination. In contrast with conventional redox mediators, Tri-Ag NPs_TSC-GSH/GSSG provided more admirable EC performance along with a lower oxidation potential (∼0.14 V). Taking advantage of the split-type mode, the immune response in a 96-well microplate was independent from EC detection, which could effectively eliminate the biological interference and thereby greatly enhance the sensitivity. As for the surface engineering process of Tri-Ag NPs, it was composed of partial GSH replacement and the formation of the GSH/GSSG surface mixed state. Primarily, the signal response of Ag NPs_TSC-GSH decreased due to the hindrance of GSH on electron transfer. Moreover, varying proportions of GSH/GSSG could further impede the oxidation process of Tri-Ag NPs_TSC-GSH/GSSG and eventually realize efficient dual signal quenching of this system. Notably, the ZIF-67@MIL-88B-GO_x nanocomposite as the label was applied for a cascade reaction system with GSH peroxidase-like activities to form the optimal GSH/GSSG proportion, causing sensitive changes in signal response with a range of different antigen concentrations. On this basis, the fabricated biosensor provided measurable outputs of aflatoxin B1 concentrations in a linear range of 0.0005-50 ng/mL with a low detection limit of 0.61 pg/mL (S/N = 3). All of the results indicated that the novel biosensor could be a promising analytical tool for future biomarker detection.

Self-powered photoelectrochemical biosensor with inherent potential for charge carriers drive

Self-powered photoelectrochemical (PEC) sensing platform without external voltage has provided a breakthrough in the development of biosensors, however, it is necessary to find suitable Fermi energy level difference between photoanode materials and photocathode materials as the driving force. Herein, the self-powered PEC sensor was developed to combine the advantages of both the photoanode (SnS₂/In₂S₃) and the photocathode (CuInS₂). The sufficient Fermi level differentiation between the photoanode with the photocathode not only resulted in an evident photocurrent response vis tuning the electron transfer but avoided redox reactions of extra electron donors/acceptors to enhance the accuracy of the sensor. The biological target was immobilized on the photocathode, which allowed the sensor to possess a good anti-interference capability for the detection of real samples. The proposed PEC sensor exhibits good sensitivity for the cytokeratin 19 fragment (CYFRA21-1) detection and a low limit of detection (LOD) of 6.57 fg mL^-1. Moreover, the as-purposed PEC system with good anti-interference capability and accuracy has implications for the detection of other biomarkers.

Electrochemical Signal Substance for Multiplexed Immunosensing Interface Construction: A Mini Review

Appropriate labeling method of signal substance is necessary for the construction of multiplexed electrochemical immunosensing interface to enhance the specificity for the diagnosis of cancer. So far, various electrochemical substances, including organic molecules, metal ions, metal nanoparticles, Prussian blue, and other methods for an electrochemical signal generation have been successfully applied in multiplexed biosensor designing. However, few works have been reported on the summary of electrochemical signal substance applied in constructing multiplexed immunosensing interface. Herein, according to the classification of labeled electrochemical signal substance, this review has summarized the recent state-of-art development for the designing of electrochemical immunosensing interface for simultaneous detection of multiple tumor markers. After that, the conclusion and prospects for future applications of electrochemical signal substances in multiplexed immunosensors are also discussed. The current review can provide a comprehensive summary of signal substance selection for workers researched in electrochemical sensors, and further, make contributions for the designing of multiplexed electrochemical immunosensing interface with well signal.

A capillary-driven LoC-SERS device integrated with catalytic hairpin assembly amplification technology for NSCLC-related biomarkers detection

A capillary-driven LoC-SERS device is fabricated for the ultrasensitive detection of NSCLC-related protein biomarkers with catalytic hairpin assembly as the signal amplification strategy.

Redox Host-Guest Nanosensors Installed with DNA Gatekeepers for Immobilization-Free and Ratiometric Electrochemical Detection of miRNA

Electrochemical nanosensors by integrating functional nucleic acids and nanomaterials hold a great promise in the fast detection of biomarkers, yet the current systems possess limitations on the accessibility of target-probe and probe-electrode interactions and the repeatability of detection. Herein, a host-guest assembly strategy is developed to build redox nanosensors for an immobilization-free and ratiometric electrochemical detection system. Specifically, electroactive molecule (E_m ) guests are loaded in porous hosts of polydopamine nanoparticles (MPDA) to act as dual-signal redox reporters. Hybrid DNA probes of G-quadruplex and a single-stranded anchor DNA are installed as gatekeepers for sealing the mesopores. Thereby, miRNA triggered E_m release by strand displacement reactions and the homogeneous transportation of the hosts/guests to the electrode facilitate the generation of reference signal/response signal at different potentials. Concomitantly applied NIR irradiation boosts the electron transfer from MPDA to the electrode and results in a tenfold increase in the reference signal. Finally, the sensing system through the differential pulse voltammetry method achieves a highly repeatable detection (relative standard deviation 3.8%) of miRNA with a lower detection limit (362 × 10^-15 m). This attractive system paves the way for rational designs of advanced electrochemical biosensors and smart diagnosis.

A ratiometric electrochemical biosensor for glycated albumin detection based on enhanced nanozyme catalysis of cuprous oxide-modified reduced graphene oxide nanocomposites

Nanozymes have enzyme-like characteristics and nanozyme-based electrochemical sensors have been widely studied for biomarker detection. In this work, cuprous oxide-modified reduced graphene oxide (Cu₂O-rGO) nanozyme was prepared by simultaneous reduction of copper chloride and graphene oxide. This Cu₂O-rGO nanozyme displayed an outstanding electrocatalytic activity to glucose oxidation and was used as the modified material of a glassy carbon electrode to fabricate an electrochemical ratiometric biosensor for glycated albumin (GA) detection. In this ratiometric biosensor, methylene blue-labeled DNA tripods (MB-tDNA) were adsorbed on the Cu₂O-rGO/GCE surface to form a bioinspired electrode (MB-tDNA/Cu₂O-rGO/GCE), in which the catalytic sites of Cu₂O-rGO were covered by MB-tDNA. In the presence of target GA, GA could be identified by the aptamer sequence contained in MB-tDNA, and a MB-tDNA/GA complex was formed and released into the solution, so the reduced current of MB-tDNA was decreased. Simultaneously, the oxidized current of the outer added glucose was increased since more catalytic sites of Cu₂O-rGO nanozyme on the substrate electrode surface were exposed. The ratio of the peak currents of glucose oxidation and methylene blue reduction (I_Glu/I_MB) was used to monitor the GA level and ultimately improve the accuracy of the method. The electrochemical sensor showed a low detection limit of 0.007 μg mL^-1 and a wide linear range from 0.02 to 1500 μg mL^-1. The proposed sensor was also successfully used to measure the GA expression level in the blood serum of a diabetic mouse model.

An ultrasensitive ratiometric immunosensor based on the ratios of conjugated distyrylbenzene derivative nanosheets with AIECL properties and electrochemical signal for CYFRA21-1 detection

Aggregation-induced electrochemiluminescence reagent, a distyrylbenzene derivative with donor-acceptor conjugated nanosheet structure, namely TPAPCN, was used as a trace label and modified on the electrode through the formation of classical sandwich complex of antibody-antigen-antibody in this work. In aggregate state, TPAPCN with twisted structure was limited in nanometer space through intermolecular π - π stacking interactions, which not only restricts the intramolecular motions but also combines a large number of singlet excitons to greatly trigger electrochemiluminescence (ECL). The ECL signal of this system enhanced with more captured cytokeratin 19 fragment 21-1 (CYFRA21-1) on the modified electrode. Three-dimensional graphene/platinum nanoparticles with large specific surface, and excellent electroconductivity and biocompatibility were prepared and acted as excellent carriers for thionine handling (3D-GN/PtNPs/Th), which was employed for improving the loading of antibodies and generating internal electrochemical signal. Consequently, a novel ratiometric sandwich immunosensor for CYFRA21-1 detection was fabricated based on TPAPCN and 3D-GN/PtNPs/Th, that is, a rapid and reliable detection was achieved through the ratio between ECL and electrochemical signals. The prepared sensor performed good linearity in the range of 50 fg/mL to 1 ng/mL with a detection limit as low as 16 fg/mL. Moreover, the detection results revealed well in the analysis of human serum samples, demonstrating a significant application for clinical monitoring and biomolecules detection.

A novel electrochemical biosensor for lung cancer-related gene detection based on copper ferrite-enhanced photoinitiated chain-growth amplification

We reported an electrochemical biosensor via CuFe₂O₄-enhanced photoinitiated chain-growth polymerization for ultrasensitive detection of lung cancer-related gene. In this work, photoinitiated atom transfer radical polymerization (ATRP) was applied to amplify the electrochemical signal corresponding to lung cancer-related gene, and polymerization was triggered off under the illumination of blue light which was involved in copper-mediated reductive quenching cycle. At the same time, CuFe₂O₄-H₂O₂ system was also activated to enhance polymerization based on the photocatalysis of CuFe₂O₄, which was based on the reaction between •OH and methacrylic monomers to generate carbon-based radicals. Numerous ferrocene-based polymer was graft onto electrode surface through this amplification stages. The limit of detection was low to 1.98 aM (in 10 μL, ∼11.9 molecules) (R² = 0.998) with a wide linear range from 0.1 fM to 10 pM. This strategy made a good trade-off between cost-effectiveness and sensitivity, and it also presented a high selectivity and anti-interference. In addition, the operation was greatly simplified and detection time was also shortened, which endowed this electrochemical DNA biosensor great application potential.

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.