DNA Enzyme-Decorated DNA Nanoladders as Enhancer for Peptide Cleavage-Based Electrochemical Biosensor

Dual-mode DNA nano-stage biosensing platform for efficient detection of uracil-DNA glycosylase activity in cells

Analyzing uracil-DNA glycosylase (UDG) activity is essential for understanding DNA repair mechanisms in disease progression and treatment. This study presents a dual-mode DNA nano-stage biosensing platform integrating electrochemiluminescence (ECL) and electrochemical impedance spectroscopy (EIS) for highly sensitive and specific UDG detection. A DNA-prism-modified electrode immobilizes UDG-responsive elements, forming a stable and efficient detection interface. Upon UDG cleavage, released DNA fragments initiate rapid nano-stage assembly, significantly amplifying the signal output. ECL signals are produced by embedded [Ru(phen)3]2+ complexes, while EIS signals result from the reaction of 3,3'-diaminobenzidine (DAB) with H2O2, catalyzed by manganese tetrakis(4-N-methylpyridyl)porphyrin (MnTMPyP). The platform achieves an exceptional detection limit of 1.0 × 10-5 U/mL, effectively validating the inhibitory effects of UDG inhibitors. Furthermore, a strong correlation between UDG activity and HeLa cell number is demonstrated. Compared to a commercial UDG detection kit, the biosensor exhibits comparable sensitivity with enhanced versatility. Notably, UDG activity is significantly higher in cancerous cells than in normal cells, reflecting the increased DNA repair demand in malignancy. This capability to distinguish UDG activity among different cell types highlights its potential for cancer diagnostics, while this biosensor platform shows promise for broader applications in clinical diagnostics, cancer research, and drug discovery.

Coordination-Based Site-Specific Labeling Strategy for Electrogenerated Chemiluminescence Biosensing of Matrix Metalloproteinase 2

Matrix metalloproteinase 2 (MMP-2) is an important biomarker for some diseases. Herein, one first-case coordination-based site-specific labeling strategy is proposed for electrogenerated chemiluminescence (ECL) biosensing of MMP-2 by employing an iridium(III) solvent complex as a signal reagent and a histidine (His)-containing peptide as a molecular recognition substrate. One ECL probe was prepared via coordination labeling of the His-containing peptide with one iridium(III) solvent complex ([(3-(2-pyridyl)benzoic acid)2Ir(DMSO)Cl], Ir1-DMSO). High ECL efficiency and good cleavage ability by MMP-2 were obtained for the ECL probe. By combining the high sensitivity of the ECL method, the good specificity of the peptide, and the simpleness of the magnetic bead-based assay, one "cleavage-magnetic enrichment type" ECL biosensing method was developed to detect MMP-2. MMP-2 can be sensitively detected in the linear range of 1.0-10 ng/mL with a limit of quantification of 1.0 ng/mL and a limit of detection of 0.3 ng/mL. Moreover, the ECL biosensing method was successfully applied for the determination of MMP-2 in serum samples with recoveries from 98.0% ± 8.0% to 108.0% ± 6.0%. Further, high affinity (Kd = 0.11 nM) was obtained for the Ir1-DMSO-labeled His-containing peptide and MMP-2. This work may pave the way for the labeling of His-containing biomolecules with an iridium(III) solvent complex and provides a promising method in point-of-care testing of MMP-2.

Fabrication of an innovative electrochemical sensor based on graphene-coated silver nanoparticles decorated over graphitic carbon nitride for efficient determination of estradiol

Monitoring small amount of endocrine disrupting chemical, estradiol (E2) residue in environmental and biological samples is extremely important because of its possible connections to breast and prostate malignancies and gastrointestinal disorders. The newly synthesized graphene-coated silver nanoparticles (GN@Ag) decorated on graphitic carbon nitride (g-C3N4)-based hybrid nanomaterial (GN@Ag/g-C3N4) was used to modify glassy carbon electrode (GCE) for electroanalytical measurement of E2. The GN@Ag/g-C3N4 nanocomposite prepared through ultrasonic-assisted reflux methodology was characterized using various physicochemical methods. The scanning electron microscopy and transmission electron microscopy have shown that GN@Ag nanoparticles were decorated and randomly dispersed over g-C3N4 sheets. The exceptional electrochemical response towards the oxidation of E2 was observed through cyclic voltammetry due to the quick electron transfer ability and superior conductivity of GN@Ag/g-C3N4/GCE. The detection limit was found to be 0.002 μM with wide linear range of E2 concentration (0.005-8.0 μM) along with remarkable stability of the fabricated electrode for 21 days showing 91% retention in initial current. The kinetic parameters such as catalytic rate constant and diffusion coefficient for E2 were estimated to be 1.1 × 105 M-1 s-1 and 1.9 × 10-4 cm2 s-1, respectively, by employing chronoamperometry. The proposed sensor also demonstrated its practical applicability for E2 determination in environmental and biological samples with a recovery range of 95-104%. Furthermore, the developed sensing platform is much better compared to reported methods in terms of simplicity, accuracy, detection limit, linearity range, and usefulness in real sample for E2 sensing.

2D graphene-based advanced nanoarchitectonics for electrochemical biosensors: Applications in cancer biomarker detection

Low-cost, rapid, and easy-to-use biosensors for various cancer biomarkers are of utmost importance in detecting cancer biomarkers for early-stage metastasis control and efficient diagnosis. The molecular complexity of cancer biomarkers is overwhelming, thus, the repeatability and reproducibility of measurements by biosensors are critical factors. Electrochemical biosensors are attractive alternatives in cancer diagnosis due to their low cost, simple operation, and promising analytical figures of merit. Recently graphene-derived nanostructures have been used extensively for the fabrication of electrochemical biosensors because of their unique physicochemical properties, including the high electrical conductivity, adsorption capacity, low cost and ease of mass production, presence of oxygen-containing functional groups that facilitate the bioreceptor immobilization, increased flexibility and mechanical strength, low cellular toxicity. Indeed, these properties make them advantageous compared to other alternatives. However, some drawbacks must be overcome to extend their use, such as poor and uncontrollable deposition on the substrate due to the low dispersity of some graphene materials and irreproducibility of the results because of the differences in various batches of the produced graphene materials. This review has documented the most recently developed strategies for electrochemical sensor fabrication. It differs in the categorization method compared to published works to draw greater attention to the wide opportunities of graphene nanomaterials for biological applications. Limitations and future scopes are discussed to advance the integration of novel technologies such as artificial intelligence, the internet of medical things, and triboelectric nanogenerators to eventually increase efficacy and efficiency.

A disposable immunosensor for the detection of salivary MMP-8 as biomarker of periodontitis

This work describes the development of a novel voltammetric immunosensor for the detection of salivary MMP-8 at the point-of-care. The electrochemical platform was based on a graphene (GPH) screen-printed electrode (SPE) functionalized by gold-nanospheres (AuNSs) and antibodies against MMP-8 protein (anti-MMP-8). The functionalization with anti-MMP-8 was realized by using 11-mercaptoundecanoic acid (11-MUA), thanks to its ability to give strong sulfur bonds with its -SH end, and to cross-link the -NH2 groups of the antibody molecule with the other -COOH end, using the traditional EDC-NHS method. The voltammetric sensor showed good performances with a linear range of 2.5-300 ng mL-1, a LOD value of 1.0 ± 0.1 ng mL-1 and a sensitivity of 0.05 µA mL cm-2 ng-1. Moreover, the proposed immunosensor was tested in real saliva samples, showing comparable results to those obtained with the conventional ELISA method. The biosensor was single-use and cost-effective and required a small quantity of test medium and a short preparation time, representing a very attractive biosensor for MMP-8 detection in human saliva.

Target-induced hot spot construction for sensitive and selective surface-enhanced Raman scattering detection of matrix metalloproteinase MMP-9

Studies have found that matrix metalloproteinase-9 (MMP-9) plays a significant role in cancer cell invasion, metastasis, and tumor growth. But it is a challenge to go for highly sensitive and selective detection and targeting of MMP-9 due to the similar structure and function of the MMP proteins family. Herein, a novel surface-enhanced Raman scattering (SERS) sensing strategy was developed based on the aptamer-induced SERS "hot spot" formation for the extremely sensitive and selective determination of MMP-9. To develop the nanosensor, one group of gold nanospheres was modified with MMP-9 aptamer and its complementary strand DNA1, while DNA2 (complementary to DNA1) and the probe molecule 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB) were grafted on the surface of the other group of gold nanospheres. In the absence of MMP-9, DTNB located on the 13-nm gold nanospheres has only generated a very weak SERS signal. However, when MMP-9 is present, the aptamer preferentially binds to the MMP-9 to construct MMP-9-aptamer complex. The bare DNA1 can recognize and bind to DNA2, which causes them to move in close proximity and create a SERS hot spot effect. Due to this action, the SERS signal of DTNB located at the nanoparticle gap is greatly enhanced, achieving highly sensitive detection of MMP-9. Since the hot spot effect is caused by the aptamer that specifically recognizes MMP-9, the approach exhibits excellent selectivity for MMP-9 detection. Based on the benefits of both high sensitivity and excellent selectivity, this method was used to distinguish the difference in MMP-9 levels between normal and cancer cells as well as the expression of MMP-9 from cancer cells with different degrees of metastasis. In addition, this strategy can accurately reflect the dynamic changes in intracellular MMP-9 levels, stimulated by the MMP-9 activator and inhibitor. This strategy is expected to be transformed into a new technique for diagnosis of specific cancers related to MMP-9 and assessing the extent of cancer occurrence, development and metastasis.

Biosensing Platform for the Detection of Biomarkers for ALI/ARDS in Bronchoalveolar Lavage Fluid of LPS Mice Model

Acute respiratory distress syndrome (ARDS) is a worldwide health concern. The pathophysiological features of ALI/ARDS include a pulmonary immunological response. The development of a rapid and low-cost biosensing platform for the detection of ARDS is urgently needed. In this study, we report the development of a paper-based multiplexed sensing platform to detect human NE, PR3 and MMP-2 proteases. Through monitoring the three proteases in infected mice after the intra-nasal administration of LPS, we showed that these proteases played an essential role in ALI/ARDS. The paper-based sensor utilized a colorimetric detection approach based on the cleavage of peptide-magnetic nanoparticle conjugates, which led to a change in the gold nanoparticle-modified paper sensor. The multiplexing of human NE, PR3 and MMP-2 proteases was tested and compared after 30 min, 2 h, 4 h and 24 h of LPS administration. The multiplexing platform of the three analytes led to relatively marked peptide cleavage occurring only after 30 min and 24 h. The results demonstrated that MMP-2, PR3 and human NE can provide a promising biosensing platform for ALI/ARDS in infected mice at different stages. MMP-2 was detected at all stages (30 min-24 h); however, the detection of human NE and PR3 can be useful for early- (30 min) and late-stage (24 h) detection of ALI/ARDS. Further studies are necessary to apply these potential diagnostic biosensing platforms to detect ARDS in patients.

Cu2+@NMOFs-to-bimetallic CuFe PBA transformation: An instant catalyst with oxidase-mimicking activity for highly sensitive impedimetric biosensor

In this work, a facile impedance biosensor was constructed for sensitive assaying of miRNA-10b based on the Cu²⁺ modified NH₂-metal organic frameworks (NMOF@Cu²⁺) coupling with a three-dimensional (3D) DNA walker signal amplification strategy. Specifically, abundant Cu²⁺ can adhere to the MOF via the coordination reaction between NH₂ and Cu²⁺, which can be applied as a skeleton to produce CuFe Prussian blue analogue@NMOF (CuFe PBA@NMOF) just in time. Meanwhile, the carboxyl group, which is rich in the organic ligands of the NMOF, can be used to assemble DNA strands (complementary strand, CS) (CS-NMOF@Cu²⁺) for biorecognition reaction. With the introduction of the target, a 3D DNA walker was triggered to shear out large amounts of assistant strands (AS), which were then anchored on the surface of GCE. Afterward, CS-NMOF@Cu²⁺ can be assembled on the GCE by hybridization with AS. Eventually, abundant CuFe PBA@NMOF were generated in situ on the electrode with the help of K₃[Fe(CN)₆], which can catalyze the 4-chloro-1-naphthol (4-CN) precipitation without H₂O₂, thereby increasing the resistance of the platform. Under the optimal conditions, the EIS biosensor presents reliable analytical performance in a wide linear range from 0.8 pM to 250 pM with a low detection limit of 0.5 pM.

MXene Enhanced Photoactivity of Bi2O3/Bi2S3 Heterojunction with G-wire Superstructure for Photoelectrochemical Detection of TET1 Protein

Ten-eleven translocation 1 (TET1) protein has the potential to accelerate the oxygenation of 5-methylcytosine to 5-hydroxymethylcytosine (5hmC); then the -CH₂OH of 5hmC can further covalently react with -SH catalyzed by M.HhaI methyltransferase. A brand-new photoelectrochemical (PEC) detection technique for the TET1 protein was created in light of this. For this objective, the Bi₂O₃/Bi₂S₃ heterojunction was first prepared by a one-pot hydrothermal method and served for photosensitive materials. For further enhancing the photoactivity, Bi₂O₃/Bi₂S₃ was blended with MXene to form an energy band-matched structure, thus improving the migration kinetics of photogenerated carriers. For achieving a high sensitivity of detection, a DNA Walker incorporated with the nicking endonuclease (Nb.BbvCI enzyme)-assisted signal amplification strategy was presented to output exponential G-quadruplex fragments. Self-assembly of the free G-quadruplex sequence into a G-wire superstructure with the assistance of Mg²⁺ provided more loading sites for MB and amplified the PEC signal. The linear range of the biosensor was 0.1-10 μg/mL with a detection limit of 0.024 μg/mL (S/N = 3) for TET1 protein under optimal experimental conditions. The suitability of the proposed method was evaluated by inhibitor screening experiments and the influence of environmental degradation on the activity of TET1 protein.

Diagnosis Biomarkers of Cholangiocarcinoma in Human Bile: An Evidence-Based Study

Simple Summary

A liquid biopsy has the characteristics of low trauma and easy acquisition in the diagnosis of cholangiocarcinoma. Many researchers try to find diagnostic or prognostic biomarkers of CCA through blood, urine, bile and other body fluids. Due to the close proximity of bile to the lesion and the stable nature, bile gradually comes into people’s view. The evaluation of human bile diagnostic biomarkers is not only to the benefit of screening more suitable clinical markers but also of exploring the pathological changes of the disease.

Abstract

Cholangiocarcinoma (CCA) is a multifactorial malignant tumor of the biliary tract, and the incidence of CCA is increasing in recent years. At present, the diagnosis of CCA mainly depends on imaging and invasive examination, with limited specificity and sensitivity and late detection. The early diagnosis of CCA always faces the dilemma of lacking specific diagnostic biomarkers. Non-invasive methods to assess the degree of CAA have been developed throughout the last decades. Among the many specimens looking for CCA biomarkers, bile has gotten a lot of attention lately. This paper mainly summarizes the recent developments in the current research on the diagnostic biomarkers for CCA in human bile at the levels of the gene, protein, metabolite, extracellular vesicles and volatile organic compounds.

Antifouling peptides combined with recognizing DNA probes for ultralow fouling electrochemical detection of cancer biomarkers in human bodily fluids

Herein, a universal strategy for the construction of highly sensitive and low fouling biosensors was proposed based on antifouling peptides conjugated with recognizing DNA probes. The peptide-DNA conjugate was formed through a reagent-free click reaction between a typical DNA aptamer modified with 5'-dibenzocyclooctyne (DBCO) and the designed antifouling peptide terminated with biotin and the azide group at its two ends. With the assistance of streptavidin (SA), the electrochemical biosensor was constructed via immobilization of the straight peptides and peptide-DNA conjugates in sequence onto the electrode surface modified with electrodeposited poly(3,4-ethylenedioxythiophene) (PEDOT) and gold nanoparticles (AuNPs). The prepared biosensor exhibited excellent antifouling performances in various human bodily fluids such as serum, sweat and urine, with a wide linear response range for CA125 from 0.01 U mL^-1 to 1000 U mL^-1, and a low limit of detection of 0.003 U mL^-1. Combining the advantages of the antifouling peptide and recognizing DNA probe, this sensing strategy was capable of assaying CA125 in undiluted human serum, and it also offered a highly promising way for the development of different antifouling biosensors through the conjugation of antifouling peptides with various DNA probes.

Electrochemical nanobiosensors equipped with peptides: a review

Recent research in the field of electrochemical biosensors equipped with peptides and nanomaterials have been categorized, reviewed, and critically analyzed. Indeed, using these innovative biosensors can revolutionize biomedical diagnostics in the future. Saving lives, time, and money in this field will be considered as some main benefits of this type of diagnosis. Here, these biosensors have been categorized and evaluated in four main sections. In the first section, the focus is on investigating the types of electrochemical peptide-based nanobiosensors applied to detect pathogenic microorganisms, microbial toxins, and viruses. In the second section, due to the importance of rapid diagnosis and prognosis of various cancers, the electrochemical peptide-based nanobiosensors designed to detect cancer biomarkers have been reviewed and analyzed. In the third section, the electrochemical peptide-based nanobiosensors, which were applied to detect the essential and effective biomolecules in the various diseases, and health control, including enzymes, hormones, biomarkers, and other biomolecules, have been considered. Finally, using a comprehensive analysis, all the used elements in these biosensors have been presented as conceptual diagrams that can effectively guide researchers in future developments. The essential factors in evaluating and analyzing these electrochemical peptide-based nanobiosensors such as analyte, peptide sequence, functional groups interacted between the peptide sequences and other biosensing components, the applied nanomaterials, diagnostic techniques, detection range, and limit of detection have also been included. Other analyzable items such as the type of used redox marker and the location of the peptide sequence against the signal transducer were also considered.

Enzymatic cleavage of specific dipeptide conjugated with ferrocene as a flexible ultra-sensitive and fast voltammetric assay of matrix metalloproteinase-9 considered a prognostic cancer biomarker in plasma samples

Studies over the last decade have shown that matrix metalloproteinases (MMPs) play a key role in the growth and metastasis of cancer. This zinc-dependent family of endopeptidases is crucial for the degradation of extracellular matrix (ECM), as well as serves as important ECM transducers which have been recognized as early biomarkers for both cancer diagnosis and treatment. In this study, we designed a new type of voltammetric biosensor, composed of a glycine-methionine dipeptide conjugated covalently to ferrocene (Gly-Met-Fc), for fast and ultrasensitive detection of the active form of MMP-9 in plasma samples. The detection was based on specific enzymatic cleavage of the Gly-Met peptide bond, which was monitored by voltammetry and gravimetry measurements. The ferrocene units act as voltammetric visualizers for the detection process. The cysteamine layer directly anchored to the gold surface ensured that the packing density of Gly-Met-Fc in the receptor layer was appropriate for the sensitive detection of MMP-9 in its active form. The developed biosensor was characterized by the widest analytical range (2.0·10^-6 - 5.0 μg⋅mL^-1) and low detection limit (0.04 pg⋅mL^-1). Another valuable feature of the proposed biosensor is that it can be applied directly to the plasma samples without any additional preparation step and thus speeds up the analysis.

Electrochemical detection of matrix metalloproteinase-7 using an immunoassay on a methylene blue/2D MoS2/graphene oxide electrode

Methylene blue (MB) adsorption onto a two-dimensional molybdenum disulfide (2D MoS₂)/graphene oxide (GO) nanocomposite sitting on a screen-printed carbon electrode (SPCE) is used to develop a new sensitive label-free electrochemical immunosensor for the detection of matrix metalloproteinase-7 (MMP-7) cancer biomarkers. The 2D MoS₂/GO nanocomposite deposited onto an SPCE provides a large specific surface area, fast electron transfer, and exceptional electrical conductivity. Furthermore, MB adsorbed onto the 2D MoS₂/GO nanocomposite architecture can be used for signal amplification in electrochemical immunosensors. Moreover, an immunosensor platform was fabricated by the adsorption of anti-MMP-7 capture antibodies onto the MB/2D MoS₂/GO nanocomposite surface via electrostatic interactions for the detection of the MMP-7 immunocomplex. Under optimum conditions, the label-free immunosensor exhibits a decrease in the current response for MB corresponding to the MMP-7 concentration. The sensor affords a linear logarithmic range of 0.010-75 ng mL^-1 with a limit of detection (LOD) of 0.007 ng mL^-1. The developed electrochemical immunosensor provides high selectivity, good reproducibility, and excellent stability. Furthermore, the proposed immunosensor can be applied for the detection of MMP-7 in human serum samples with good recovery. Thus, this device can be applied for the early clinical diagnosis of pancreatic and colorectal cancers.

Gold Nanoparticles: Multifaceted Roles in the Management of Autoimmune Disorders

Gold nanoparticles (GNPs) have been recently applied for various diagnostic and therapeutic purposes. The unique properties of these nanoparticles (NPs), such as relative ease of synthesis in various sizes, shapes and charges, stability, high drug-loading capacity and relative availability for modification accompanied by non-cytotoxicity and biocompatibility, make them an ideal field of research in bio-nanotechnology. Moreover, their potential to alleviate various inflammatory factors, nitrite species, and reactive oxygen production and the capacity to deliver therapeutic agents has attracted attention for further studies in inflammatory and autoimmune disorders. Furthermore, the characteristics of GNPs and surface modification can modulate their toxicity, biodistribution, biocompatibility, and effects. This review discusses in vitro and in vivo effects of GNPs and their functionalized forms in managing various autoimmune disorders (Ads) such as rheumatoid arthritis, type 1 diabetes, and multiple sclerosis.

A label-free ratiometric immunoassay using bioinspired nanochannels and a smart modified electrode

Labeling with redox reporter is often required in developing electrochemical bioassay for most proteins or nucleic acid biomarkers. Herein, a label-free ratiometric immunosensing platform is firstly developed by integrating the antibody-conjugated nanochannels with a smart modified electrode. The electrode modifier is the composite of C₆₀, tetraoctylammonium bromide (TOA⁺) and Prussian blue (PB). Cyclic voltammograms of the ultimate C₆₀-TOA⁺/PB modified electrode exhibited two pairs of peaks at 0.15 V and -0.13 V, ascribing to the redox of PB and C₆₀, respectively. With the addition of K₃[Fe(CN)₆] in the electrolyte solution, the peaks of PB decreased due to the adsorption of [Fe(CN)₆]^3- while the peaks of C₆₀ increased because of the formation of the ternary complex (TC) C₆₀-TOA⁺-[Fe(CN)₆]^3-. As a result, the peak current ratio I_PB/I_TC decreased gradually with the increment of the concentration of [Fe(CN)₆]^3-. For the nanochannels-based immunosensing platform, the steric hindrance of the bioconjugated nanochannels varied with the loading amount of the target CA125, and thus [Fe(CN)₆]^3- passing through the channels was quantitatively affected. And the higher CA125 level was, the less [Fe(CN)₆]^3- concentration was. And thus, the ratio I_PB/I_TC monitored at the C₆₀-TOA⁺/PB modified electrode increased with the increase of the concentration of CA125. The ratiometric immunoassay featured a linear calibration range from 1.0 U mL^-1 to 100 U mL^-1 with a low detection limit of 0.86 U mL^-1. In addition, the ratiometric immunosensing platform demonstrated good specificity and stability as well as acceptable accuracy in overcoming the effect of electrode passivation which was an inherent problem of electroanalysis.

Biosensors and bioassays for determination of matrix metalloproteinases: state of the art and recent advances

Matrix metalloproteinases (MMPs) are closely associated with various physiological and pathological processes, and have been regarded as potential biomarkers for severe diseases including cancer. Accurate determination of MMPs would advance our understanding of their roles in disease progression, and is of great significance for disease diagnosis, treatment and prognosis. In this review, we present a comprehensive overview of the developed bioassays/biosensors for detection of MMPs, and highlight the recent advancement in nanomaterial-based immunoassays for MMP abundance measurements and nanomaterial-based biosensors for MMP activity determination. Enzyme-linked immunosorbent assay (ELISA)-based immunoassays provide information about total levels of MMPs with high specificity and sensitivity, while target-based biosensors measure the amounts of active MMPs, and allow imaging of MMP activities in vivo. For multiplex and high-throughput analysis of MMPs, microfluidics and microarray-based assays are described. Additionally, we put forward the existing challenges and future prospects from our perspective.

Peptide-based electrochemical biosensors utilized for protein detection

Proteins are generally detected as biomarkers for tracing or determining various disorders in organisms. Biomarker proteins can be tracked in samples with various origins and in different concentrations, revealing whether an organism is in a healthy or unhealthy state. In regard to detection, electrochemical biosensors are a potential fusion of electronics, chemistry, and biology, allowing for fast and early point-of-care detection from a biological sample with the advantages of high sensitivity, simple construction, and easy operation. Peptides present a promising approach as a biorecognition element when connected with electrochemical biosensors. The benefits of short peptides lie mainly in their good stability and selective affinity to a target analyte. Therefore, peptide-based electrochemical biosensors (PBEBs) represent an alternative approach for the detection of different protein biomarkers. This review provides a summary of the past decade of recently proposed PBEBs designed for protein detection, dividing them according to different protein types: (i) enzyme detection, including proteases and kinases; (ii) antibody detection; and (iii) other protein detection. According to these protein types, different sensing mechanisms are discussed, such as the peptide cleavage by a proteases, phosphorylation by kinases, presence of antibodies, and exploiting of affinities; furthermore, measurements are obtained by different electrochemical methods. A discussion and comparison of various constructions, modifications, immobilization strategies and different sensing techniques in terms of high sensitivity, selectivity, repeatability, and potential for practical application are presented.

A novel impedance enhancer for amperometric biosensor based ultrasensitive detection of matrix metalloproteinase-2

The detection range and sensitivity is crucial to the determination of tumor markers. For amperometric biosensors, the detection range relies on the initial current signals (I₀) and the sensitivity is tightly related to the current signals difference (ΔI) caused by per unit concentration target. Herein, an amperometric biosensor was fabricated using polyaniline gel as substrate and CS-AuNPs-Pb²⁺ as impedance enhancer. The sensing substrate exhibited strong current signal in [Fe(CN)₆]^3-/4- due to the excellent conductivity and large specific surface area of polyaniline gel. CS-AuNPs-Pb²⁺ with large hindrance effect can significantly increase interfacial resistance, resulting in the enhancement of ΔI. In addition, Pb²⁺ can react with sodium tartrate to produce non-conducting sodium tartrate gel on sensing interface, leading to further amplification of ΔI. Matrix metalloproteinase-2 (MMP-2) was analysed to prove the feasibility of this strategy. The proposed amperometric biosensor reveal both wide linear detection range from 1 pg mL^-1 to 1 μg mL^-1 and high sensitivity of 28.4 μA·(LgC_MMP-2)^-1. Therefore, this strategy will be of great significance to design other ultrasensitive amperometric biosensors.

Ultrasensitive Electrochemical Biosensor of Bacterial 16S rRNA Gene Based on polyA DNA Probes

Traditional microbiology analysis is usually hindered by the long time-cost and lack of portability in many urgent situations. In this work, we developed a novel electrochemical DNA biosensor (E-biosensor) for sensitive analysis of the 16S rRNA gene of five bacteria, using a consecutive adenine (polyA) probe. The polyA probe consists of a polyA tail and a recognition part. The polyA tail can combine onto the gold surface with improved controllability of the surface density, by conveniently changing the length of polyA. The recognition part of the capture probe together with two biotin-labeled reporter probes hybridize with the target DNA and form a stable DNA-tetramer sandwich structure, and then avidin-HRP enzyme was added to produce a redox current signal for the following electrochemical detection. Finally, we realized sensitive quantification of artificial target DNA with a limit of detection (LOD) of 10 fM, and excellent selectivity and reusability were also demonstrated. Importantly, the detection capability was equally good when facing bacterial genomic DNA, due to the base-stacking force of our multireporter-probe system, which can help to break the second structure and stabilize the probe-target complexes. Our biosensor was constructed on a 16-channel electrode chip without any polymerase chain reaction (PCR) process needed, which took a significant step toward a portable bacteria biosensor.

Electrochemical Biosensors as Potential Diagnostic Devices for Autoimmune Diseases

An important class of biosensors is immunosensors, affinity biosensors that are based on the specific interaction between antibodies and antigens. They are classified in four classes based on the type of employed transducer: electrochemical, optical, microgravimetric, and thermometric and depending on the type of recognition elements, antibodies, aptamers, microRNAs and recently peptides are integrating parts. Those analytical devices are able to detect peptides, antibodies and proteins in various sample matrices, without many steps of sample pretreatment. Their high sensitivity, low cost and the easy integration in point of care devices assuring portability are attracting features that justify the increasing interest in their development. The use of nanomaterials, simultaneous multianalyte detection and integration on platforms to form point-of-care devices are promising tools that can be used in clinical analysis for early diagnosis and therapy monitoring in several pathologies. Taking into account the growing incidence of autoimmune disease and the importance of early diagnosis, electrochemical biosensors could represent a viable alternative to currently used diagnosis methods. Some relevant examples of electrochemical assays for autoimmune disease diagnosis developed in the last several years based on antigens, antibodies and peptides as receptors were gathered and will be discussed further.

Amperometric Biosensor of Matrix Metalloproteinase-7 Enhanced by Pd-Functionalized Carbon Nanocomposites

Matrix metalloproteinase-7 plays a pivotal role in tumour progression and metastasis as an enzyme that can degrade the cell-matrix composition and cleave peptides between alanine and leucine in various biomolecular activation processes. In this work, a Pd-functionalised carbon nanocomposite was designed as a new impedance enhancer for an amperometric sensor of MMP-7. Pd nanoparticles in the enhancer can catalyse the oxidation of 4-chloro-1-naphthol with H₂O₂ to generate insoluble precipitation in situ, forming high-resistance precipitation on electrodes. In addition, poorly conductive carbon nanospheres of the nanocomposite increased the precipitation resistance, further causing a dramatic increase in resistivity of the enhancer and, subsequently, a significant decrease in current. This can significantly promote the current signal difference between the biosensor treated with and without the target analyte, which is directly related to the sensitivity of the amperometric biosensor. Overall, electrochemical biosensor can sensitively detect MMP-7 in the range of 100 fg mL^-1 to 100 ng mL^-1 with a limit of detection for MMP-7 of 17.38 fg mL^-1.

Tailoring MWCNTs and β-Cyclodextrin for Sensitive Detection of Acetaminophen and Estrogen

Monitoring of trace amount of acetaminophen and estrogen in drinking water is of great importance because of their potential links to gastrointestinal diseases and breast and prostate cancers. The sensitive and accurate detection of acetaminophen and estrogen requires the development of advanced sensing materials that possess appropriate number of analyte-capturing sites and suitable signal conduction path. This can be achieved by implementing appropriate chemical attachment of multiwalled carbon nanotubes (MWCNTs) and β-cyclodextrin (βCD). Here, we report a systematic investigation of four types of modified MWCNT-βCD: (1) physical mixing, (2) "click reaction", (3) thionyl chloride esterification, and (4) Steglich esterification. The Steglich esterification is a one-step approach with shorter reaction time, lower reaction temperature, and eliminates handling of air/moisture-sensitive reagents. MWCNT-βCD prepared by Steglich esterification possessed moderate βCD loading (5-10 wt %), large effective surface area, and fast electron transfer. The host-guest interaction of βCD and redox properties of MWCNT enabled sensitive detection of acetaminophen and 17β-estradiol (E2 is a primary female sex hormone) in the range of 0.005-20 and 0.01-15 μM, with low detection limits of 3.3 and 2.5 nM, respectively. We demonstrated accurate detection results of pharmaceutical compositions in water and urine samples. These results indicate that Steglich esterification method may be applied in fabricating pharmaceutical contaminants sensors for health and environmental applications.

Bacterial Analysis Using an Electrochemical DNA Biosensor with Poly-Adenine-Mediated DNA Self-Assembly

The spatial arrangement of DNA probes on the electrode surface is of critical significance for the performance of electrochemical biosensors. However, rational control of the probe surface remains challenging. In this work, we develop a capture probe carrying a poly-adenine anchoring block to construct a programmable self-assembled monolayer for a "sandwich-type" electrochemical biosensor. We show that with a co-assembling strategy using a polyA capture probe and 6-mercapto-1-hexanol, the density of the probes on the gold electrode can be simply adjusted by the length of polyA. The electron-transfer effect and thus the hybridization efficiency can as well be optimized by tuning the polyA length. As a result, we obtained an excellent biosensor performance with a limit of detection as low as 5 fM for a synthetic DNA target. We demonstrate the practicability of this system by analyzing a PCR product from Escherichia coli genomic DNA (0.2 pg/μL). On the basis of the ideal electrochemical interface, our polyA-based biosensor exhibited excellent reusability and stability, which is important for potential applications in the onsite analysis for a wide range of targets.

Fluorescence Regulation of Copper Nanoclusters via DNA Template Manipulation toward Design of a High Signal-to-Noise Ratio Biosensor

Because of bioaccumulation of food chain and disability of biodegradation, concentration of toxic mercury ions (Hg²⁺) in the environment dramatically varies from picomolar to micromolar, indicating the importance of well-performed Hg²⁺ analytical methods. Herein, reticular DNA is constructed by introducing thymine (T)-Hg²⁺-T nodes in poly(T) DNA, and copper nanoclusters (CuNCs) with aggregate morphology are prepared using this reticular DNA as a template. Intriguingly, the prepared CuNCs exhibit enhanced fluorescence. Meanwhile, the reticular DNA reveals evident resistance to enzyme digestion, further clarifying the fluorescence enhancement of CuNCs. Relying on the dual function of DNA manipulation, a high signal-to-noise ratio biosensor is designed. This analytical approach can quantify Hg²⁺ in a very wide range (50 pM to 500 μM) with an ultralow detection limit (16 pM). Besides, depending on the specific interaction between Hg²⁺ and reduced l-glutathione (GSH), this biosensor is able to evaluate the inhibition of GSH toward Hg²⁺. In addition, pollution of Hg²⁺ in three lakes is tested using this method, and the obtained results are in accord with those from inductively coupled plasma mass spectrometry. In general, this work provides an alternative way to regulate the properties of DNA-templated nanomaterials and indicates the applicability of this way by fabricating an advanced biosensor.