Controllable self-cleaning FET self-assembled RNA-cleaving DNAzyme based DNA nanotree for culture-free Staphylococcus aureus detection.

Staphylococcus aureus (SA) poses a serious risk to human and animal health, necessitating a low-cost and high-performance analytical platform for point-of-care diagnostics. Cellulose paper-based field-effect transistors (FETs) with RNA-cleaving DNAzymes (RCDs) can fulfill the low-cost requirements, however, its high hydrophilicity and lipophilicity hinder biochemical modification and result in low sensitivity, poor mechanical stability and poor fouling performance. Herein, we proposed a controllable self-cleaning FET to simplify biochemical modification and improve mechanical stability and antifouling performance. Then, we constructed an RCD-based DNA nanotree to significantly enhance the sensitivity for SA detection. For controllable self-cleaning FET, 1 H,1 H,2 H,2 H-perfluorodecyltrimethoxysilane based-polymeric nanoparticles were synthesized to decorate cellulose paper and whole carbon nanofilm wires. O2 plasma was applied to regulate to reduce fluorocarbon chain density, and then control the hydrophobic-oleophobic property in sensitive areas. Because negatively charged DNA affected the sensitivity of semiconducting FETs, three Y-shaped branches with low-cost were designed and applied to synthesize an RCD-based DNA-Nanotree based on similar DNA-origami technology, which further improved the sensitivity. The trunk of DNA-Nanotree was composed of RCD, and the canopy was self-assembled using multiple Y-shaped branches. The controllable self-cleaning FET biosensor was applied for SA detection without cultivation, which had a wide linear range from 1 to 105 CFU/mL and could detect a low value of 1 CFU/mL.

Development of Molecularly Imprinted Magnetic Amino Acid-Based Nanoparticles for Voltammetric Analysis of Lead Ions in Honey.

Lead (Pb) is a hazardous metal that poses a significant threat to both the environment and human health. The presence of Pb in food products such as honey can pose a significant risk to human health and is therefore important to detect and monitor. In this study, we propose a voltammetric detection method using molecularly imprinted polymer (MIP) electrodes to detect Pb (II) ions in honey. Pb (II) ion-imprinted amino acid-based nanoparticles with magnetic properties on a carbon paste electrode (MIP-CPE) were designed to have high sensitivity and selectivity towards Pb (II) ions in the honey sample. Zetasizer measurements, electron spin resonance, and scanning electron microscopy were used to characterize magnetic polymeric nanoparticles. The results showed that the voltammetric detection method using MIP-CPE was able to accurately detect Pb (II) ions in honey samples with a low detection limit. The proposed method offers a simple, rapid, cost-effective solution for detecting Pb (II) ions in honey. It could potentially be applied to other food products to ensure their safety for human consumption. The MIP-CPE sensor was designed to have high sensitivity and selectivity towards Pb (II) ions in the honey sample. The results showed that the technique was able to deliver highly sensitive results since seven different concentrations were prepared and detected to obtain an R2 of 0.9954, in addition to a low detection limit (LOD) of 0.0912 µM and a low quantification limit (LOQ) of 0.276 µM. Importantly, the analysis revealed no trace of Pb (II) ions in the honey samples obtained from Cyprus.

An origami microfluidic paper device based on core-shell Cu@Cu2S@N-doped carbon hollow nanocubes.

BACKGROUD: The global prevalence of diabetes mellitus, a serious chronic disease with fatal consequences for millions annually, is of utmost concern. The development of efficient and simple devices for monitoring glucose levels is of utmost significance in managing diabetes. The advancement of nanotechnology has resulted in the indispensable utilization of advanced nanomaterials in high-performance glucose sensors. Modulating the morphology and intricate composition of transition metals represents a viable approach to exploit their structure/function correlation, thereby achieving optimal electrocatalytic performance of the synthesized catalysts. RESULTS: Herein, a sensitive and rapid Cu-encapsulated Cu2S@nitrogen-doped carbon (Cu@Cu2S@N-C) hollow nanocubes-functionalized microfluidic paper-based analytical device (µ-PAD) was fabricated. Through a delicate sacrificial template/interface technique and thermal decomposition, inter-connected hollow networks were formed to boost the active sites, and the carbon shell was coated to protect Cu from being oxidation. For application, the constructed µ-PAD is used for glucose sensing utilizing an origami automated sample pretreatment system enabled by a simple application of strong alkaline solution on wax paper. Under optimal circumstances, the Cu@Cu2S@N-C electrochemical biosensor exhibits broad detection range of 2-7500 µM (R2 = 0.996) with low detection limit of 0.16 µM (S/N = 3) and high sensitivity of 1996 µA mM-1 cm-2. Additionally, the constructed µ-PAD also exhibited excellent selectivity, stability, and reproducibility. SIGNIFICANCE: By rationally designing the double-shell hollow nanostructure and introducing Cu-encapsulated inner layer, the synthesized Cu@Cu2S@N-C hollow nanocubes show large specific surface area, short diffusion channels, and high stability. The proposed origami µ-PAD has been successfully applied to serum samples without any additional sample preparation steps for glucose determination, offering a new perspective for early nonenzymatic glucose diagnosis.

Green sonochemical synthesis of ZnCo2O4 decorated with carbon nanofibers for enhanced electrochemical detection of bisphenol A in food products.

The facile sonochemical synthesis is reported of zinc cobalt oxide (ZnCo2O4) composited with carbon nanofiber (CNF). Structural, chemical, and morphological were characterized by X-ray diffraction (XRD), X-ray photoluminescent spectroscopy (XPS), field emission scanning electron microscopy (FESEM), and transmittance electron microscopy (TEM), respectively. ZnCo2O4/CNF-modified GCE was applied to the detection of bisphenol A (BPA). The modified GCE shows enhanced sensing performance towards BPA, which includes a linear range (0.2 to 120 µM L-1) alongside a low limit of detection (38.2 nM L-1), low interference, and good stability. Detection of lower concentrations of BPA enables real sample analysis in the food industries (milk, orange juice, yogurt, tap water, and baby feeding bottles). Surprisingly, the BPA was detected in milk 510 nM L-1, orange juice 340 nM L-1, yogurt 1050 nM L-1, and tap water 140 nM L-1. Moreover, an interaction mechanism between the BPA analyte and ZnCo2O4 was discussed.

Lamellar Ti3C2 MXene composite decorated with platinum-doped MoS2 nanosheets as electrochemical sensing functional platform for highly sensitive analysis of organophosphorus pesticides.

Precisely detecting organophosphorus pesticides (OPs) is paramount in upholding human safety and environmental preservation, especially in food safety. Herein, an electrochemical acetylcholinesterase (AChE) sensing platform entrapped in chitosan (Chit) on the glassy carbon electrodes (GCEs) decorated with Pt/MoS2/Ti3C2 MXene (Pt/MoS2/TM) was constructed for the detection of chlorpyrifos. It is worth noting that Pt/MoS2/TM possesses good biocompatibility, remarkable electrical conductivity, environmental stability and large specific surface area. Besides, the heterostructure formed by the composite of TM and MoS2 improves the conductivity and maintains the original structure, which is conducive to improving the electrochemical property. The coordination effect between the individual components enables the even distribution of functional components and enhances the electrochemical performance of the biosensor (AChE-Chit/Pt/MoS2/TM). Under optimal efficiency and sensitivity, the AChE-Chit/Pt/MoS2/TM/GCE sensing platform exerts comparable analytical performance and a wide concentration range of chlorpyrifos from 10-12 to 10-6 M as well as a low limit of detection (4.71 × 10-13 M). Furthermore, the biosensor is utilized to detect OPs concerning three kinds of fruits and vegetables with good feasibility and recoveries (94.81% to 104.0%). This work would provide a new scheme to develop high-sensitivity sensors based on the two-dimensional nanosheet/laminar hybrid structure for practical applications in environmental monitoring and agricultural product detection.

Comparative performance analysis of mussel-inspired polydopamine, polynorepinephrine, and poly-α-methyl norepinephrine in electrochemical biosensors.

Polydopamine (PDA) has garnered significant interest for applications in biosensors, drug delivery, and tissue engineering. However, similar polycatecholamines like polynorepinephrine (PNE) with additional hydroxyl groups and poly-α-methylnorepinephrine (PAMN) with additional hydroxyl and methyl groups remain unexplored in the biosensing domain. This research introduces three innovative biosensing platforms composed of ternary nanocomposite based on reduced graphene oxide (RGO), gold nanoparticles (Au NPs), and three sister polycatecholamine compounds (PDA, PNE, and PAMN). The study compares and evaluates the performance of the three biosensing systems for the ultrasensitive detection of Mycobacterium tuberculosis (MTB). The formation of the nanocomposites was meticulously examined through UV-Visible, Raman, XRD, and FT-IR studies with FE-SEM and HR-TEM analysis. Cyclic voltammetry and differential pulse voltammetry measurements were also performed to determine the electrochemical characteristics of the modified electrodes. Electrochemical biosensing experiments reveal that the RGO-PDA-Au, RGO-PNE-Au, and RGO-PAMN-Au-based biosensors detected target DNA up to a broad detection range of 0.1 × 10-8 to 0.1 × 10-18 M, with a low detection limit (LOD) of 0.1 × 10-18, 0.1 × 10-16, and 0.1 × 10-17 M, respectively. The bioelectrodes were proved to be highly selective with excellent sensitivities of 3.62 × 10-4 mA M-1 (PDA), 7.08 × 10-4 mA M-1 (PNE), and 6.03 × 10-4 mA M-1 (PAMN). This study pioneers the exploration of two novel mussel-inspired polycatecholamines in biosensors, opening avenues for functional nanocoatings that could drive further advancements in this field.

Dual-modal biosensor for mercuric ion detection based on Cu2O@Cu2S/D-TA COF heterojunction with excellent catalase-like, electrochemical and photoelectrochemical properties.

In this study, a dual-mode biosensor based on the heterojunction of Cu2O@Cu2S/D-TA COF was constructed for ultra-sensitive detection of Hg2+ using both photoelectrochemical and electrochemical approaches. Briefly, a 2D ultra-thin covalent organic framework film (D-TA COF film) with excellent photoelectrochemical signals was prepared on ITO surfaces through an in situ growth method. Subsequently, the probe H1 was immobilized onto the biosensor via Au-S bonds. In the presence of Hg2+, the formation of T-Hg2+-T complexes triggered hybridization chain reactions (HCR), leading to the attachment of abundant Cu2O@Cu2S probes onto the biosensor. As a p-type semiconductor, Cu2O@Cu2S could form a heterojunction with the underlying D-TA COF films. Meanwhile, it exhibited catalase-like activity, and the O2 produced by its catalytic decomposition of H2O2 can interact with the D-TA COF films, thus achieving double amplification of the photocurrent signal. Benefiting from the excellent and inherent Cu2+/Cu+ redox pairs of Cu2O@Cu2S, satisfactory differential pulse voltammetry (DPV) signals were obtained. As expected, the dual-mode biosensor was realized with wider linear ranges and low detection limits. Additionally, the analytical performance for Hg2+ in real water samples was excellent. Briefly, this suggested approach offers a facile and highly efficient modality for monitoring heavy metal ions in aquatic environments.

Development and characterization of a non-enzymatic electrochemical biosensor for rapid determination of sorbent-based extracted trazodone and doxepin in complicated samples.

BACKGROUND: Given the importance of achieving optimal therapeutical concentration in patients treated with antidepressants, this study investigates a novel technique for the simultaneous determination of trazodone (TRZ) and doxepin (DOX) in human plasma and serum samples for the first time. RESULTS: To achieve simultaneous determination of two antidepressants, TRZ and DOX, a novel detection system was designed: a non-enzymatic voltammetric biosensor based on boron-reduced graphene oxide/manganese oxide nanoparticles (GCE/B-rGO/MnO NPs). The detection was accomplished after pre-concentration and extraction trace amounts of the analytes using the thin film-solid phase microextraction (TF-SPME) technique, which employed polyvinyl alcohol/polyvinyl acetate/copper oxide nanoparticles (PVA/PVAc/CuO NPs) electrospun nanofibers. The successful preparation of composite nanofibers and modified electrodes was confirmed using the evaluation of field emission-scanning electron microscopy (FE-SEM) and energy-dispersive X-ray spectroscopy (EDX). Also, the composite nanofibers were characterized with attenuated total reflectance-Fourier transform-infrared (ATR-FT-IR) and X-ray diffraction (XRD). In the solution of TRZ and DOX, under optimum experimental conditions, the linear dynamic ranges (LDRs) were 0.1-20.0 µmol L-1 and 0.5-27.0 µmol L-1, respectively. Also, the limit of detection (LOD) values of TRZ and DOX were 0.032 and 0.150 µmol L-1. SIGNIFICANCE: PVAc acts as a cross-linking agent for PVA, and their mixture is effective for sample preparation and pre-concentration of analytes in complex matrices. Also, adding CuO NPs to this polymeric mixture enhanced the adsorption efficiency. Taking advantage of the high surface area of MnO NPs and the high electrical conductivity of B-rGO, and considering the superiority of their simultaneous utilization, the constructed electrochemical biosensor is both cost-effective and rapid. It demonstrates excellent stability, repeatability, and sensitivity for the simultaneous determination of TRZ and DOX under optimal conditions. This biosensor, the first of its kind, is specifically designed for the simultaneous determination of TRZ and DOX in human plasma and serum samples, representing a significant advancement in biosensing technology.

Ultrasensitive electrochemical microRNA-21 detection based on MXene and ATRP photocatalytic strategy.

A Ti3C2TxMXene-based biosensor has been developed and the photocatalytic atom transfer radical polymerization (photo ATRP) amplification strategy applied to detect target miRNA-21 (tRNA). Initially, Ti3C2TxMXene nanosheets were synthesized from the Ti3AlC2 MAX precursor via selective aluminum etching. Then, functionalization of Ti3C2TxMXene nanosheets with 3-aminopropyl triethoxysilane (APTES) via silylation reactions to facilitate covalent bonding with hairpin DNA biomolecules specifically designed for tRNA detection. Upon binding with the tRNA, the hairpin DNA liberated the azide (N3) group, initiating a click reaction to affix to the photo ATRP initiator. Through the ATRP photoreaction, facilitated by an organic photoredox catalyst and light, a significant amount of ferrocenyl methyl methacrylate (FMMA) monomer was immobilized on the electrode. Therefore, the electrochemical signal is amplified. The electrochemical efficacy of the biosensor was assessed using square wave voltammetry (SWV). Under optimized conditions, the biosensor demonstrated remarkable sensitivity in detecting tRNA, with a linear detection range from 0.01 fM to 10 pM and a detection limit of 2.81 aM. The findings elucidate that the developed biosensor, in conjunction with the photo ATRP strategy, offers reproducibility, stability, and increased sensitivity, underscoring its potential applications within the experimental medical sector of the biomolecular industry.

Label-free electrochemical biosensor based on dual amplification of gold nanoparticles and polycaprolactones for CEA detection.

Carcinoembryonic Antigen (CEA), an acidic glycoprotein with human embryonic antigen properties, is found on the surface of cancer cells that have differentiated from endodermal cells. This paper presents a label-free electrochemical immunoassay for the dual amplification detection of CEA using gold nanoparticles loaded with polypyrrole polydopamine (Au/PPy-PDA) and polymerized polycaprolactone (Ng-PCL) prepared by ring-opening polymerization (ROP). First, the composite Au/PPy-PDA was adhered to the electrode surface. Then, gold nanoparticles form a Au-S bond with the sulfhydryl group in Apt1 to secure it on the electrode surface. Subsequently, the non-specific binding sites on the electrodes surface are closed by bovine serum albumin (BSA). Next, CEA is dropped onto the electrode surface, which is immobilized by antigen-antibody specific recognition, and the carboxyl-functionalized Apt2 forms a "sandwich structure" of antibody-antigen-antibody by specific recognition. Polymeric Ng-PCL is adhered to the electrode surface, leading to an increase in the electrochemical impedance signal, resulting in a complete chain of signal analysis. Finally, the response signal is detected by electrochemical impedance spectroscopy (EIS). Under optimal experimental conditions, the method has the advantages of high sensitivity and wide linear range (1 pg mL-1∼100 ng mL-1), and the lower limit of detection (LOD) is 0.234 pg mL-1. And it has the same high sensitivity, selectivity and interference resistance for the real samples detection. Thus, it provides a new way of thinking about biomedical and clinical diagnosis.

Role of miRNA-21 in cancer and its application in electrochemical bioanalysis.

GRAPHICAL ABSTRACT[Formula: see text].

An electrochemical biosensor based on mild reduction-activated CRISPR/Cas12a system for sensitive detection of circulating tumor cells.

Circulating tumor cell (CTC) has been a valuable biomarker for the diagnosis of breast cancer, while folate receptor is a kind of cell surface receptor glycoprotein which is overexpressed in breast cancer. In this work, we have designed and fabricated an electrochemical biosensor for sensitive detection of folate receptor-positive CTCs based on mild reduction assisted CRISPR/Cas system. Specifically, folate functionalized magnetic beads are firstly prepared to capture CTCs owing to the strong affinity between folate and the folate receptors on the surface of cells. Then, the cell membranes are treated by mild reduction so as to expose a large number of free sulfhydryl groups, which can be coupled with maleimide-DNA to introduce the signal amplified CRISPR/Cas12a system. After the trans-cleavage activity of CRISPR/Cas12a is activated, the long chain DNA modified with electroactive molecules methylene blue can be randomly cleaved into short DNA fragments, which are then captured on the graphite electrode through the host-guest recognition with cucurbit [7]uril, generating highly amplified electrochemical signal corresponding to the number of CTCs. The electrochemical biosensor not only demonstrates the sensitivity with a low detection limit of 2 cells/mL, but also highlights its excellent selectivity and stability in complex environment. Therefore, our biosensor may provide an alternative tool for the analysis of CTCs.

One-pot electrochemical detection of foodborne pathogen based on in situ nucleic acid amplification and wash-free assay.

A signal amplification electrochemical biosensor chip was developed to integrate loop-mediated isothermal amplification (LAMP) based on in situ nucleic acid amplification and methyl blue (MB) serving as the hybridization redox indicator for sensitive and selective foodborne pathogen detection without a washing step. The electrochemical biosensor chip was designed by a screen-printed carbon electrode modified with gold nanoparticles (Au NPs) and covered with polydimethylsiloxane membrane to form a microcell. The primers of the target were immobilized on the Au NPs by covalent attachment for in situ amplification. The electroactive MB was used as the electrochemical signal reporter and embedded into the double-stranded DNA (dsDNA) amplicons generated by LAMP. Differential pulse voltammetry was introduced to survey the dsDNA hybridization with MB, which differentiates the specifically electrode-unbound and -bound labels without a washing step. Pyrene as the back-filling agent can further improve response signaling by reducing non-specific adsorption. This method is operationally simple, specific, and effective. The biosensor showed a detection linear range of 102-107 CFU mL-1 with the limit of detection of 17.7 CFU mL-1 within 40 min. This method showed promise for on-site testing of foodborne pathogens and could be integrated into an all-in-one device.

Enhancing CRISPR/Cas-mediated electrochemical detection of nucleic acid using nanoparticle-labeled covalent organic frameworks reporters.

Molecular detection of nucleic acid plays an important role in early diagnosis and therapy of disease. Herein, a novel and enhanced electrochemical biosensor was exploited based on target-activated CRISPR/Cas12a system coupling with nanoparticle-labeled covalent organic frameworks (COFs) as signal reporters. Hollow spherical COFs (HCOFs) not only served as the nanocarriers of silver nanoparticles (AgNPs)-DNA conjugates for enhanced signal output but also acted as three-dimensional tracks of CRISPR/Cas12a system to improve the cleavage accessibility and efficiency. The presence of target DNA triggered the trans-cleavage activity of the CRISPR/Cas12a system, which rapidly cleaved the AgNPs-DNA conjugates on HCOFs, resulting in a remarkable decrease of the electrochemical signal. As a proof of concept, the fabricated biosensing platform realized highly sensitive and selective detection of human papillomavirus type 16 (HPV-16) DNA ranging from 100 fM to 1 nM with the detection limit of 57.2 fM. Furthermore, the proposed strategy provided a versatile and high-performance biosensor for the detection of different targets by simple modification of the crRNA protospacer, holding promising applications in disease diagnosis.

Filtered Saliva for Rapid and Accurate Analyte Detection for POC Diagnostics.

Saliva has shown considerable promise as a diagnostic medium for point-of-care (POC) and over-the-counter (OTC) diagnostic devices due to the non-invasive nature of its collection. However, a significant limitation of saliva-based detection is undesirable interference in a sensor's readout caused by interfering components in saliva. In this study, we develop standardized sample treatment procedures to eliminate bubbles and interfering molecules while preserving the sample's target molecules such as spike (S) protein and glucose. We then test the compatibility of the pretreatment system with our previously designed SARS-CoV-2 and glucose diagnostic biosensing systems for detecting S protein and glucose in subject saliva. Ultimately, the effectiveness of each filter in enhancing biomarker sensitivity is assessed. The results show that a 20 mg nylon wool (NW) filter shows an 80% change in viscosity reduction with only a 6% reduction in protein content, making it an appropriate filter for the salivary S protein diagnostic system. Meanwhile, a 30 mg cotton wool (CW) filter is identified as the optimal choice for salivary glucose detection, achieving a 90% change in viscosity reduction and a 60.7% reduction in protein content with a minimal 4.3% reduction in glucose content. The NW pretreatment filtration significantly improves the limit of detection (LOD) for salivary S protein detection by five times (from 0.5 nM to 0.1 nM) and it reduces the relative standard deviation (RSD) two times compared to unfiltered saliva. Conversely, the CW filter used for salivary glucose detection demonstrated improved linearity with an R2 of 0.99 and a sensitivity of 36.6 µA/mM·cm2, over twice as high as unfiltered saliva. This unique filtration process can be extended to any POC diagnostic system and optimized for any biomarker detection, making electrochemical POC diagnostics more viable in the current market.

Electrochemical biosensor for sensitive detection of SARS-CoV-2 gene fragments using Bi2Se3 topological insulator.

In this study, we have designed an electrochemical biosensor based on topological material Bi2Se3 for the sensitive detection of SARS-CoV-2 in the COVID-19 pandemic. Flake-shaped Bi2Se3 was obtained directly from high-quality single crystals using mechanical exfoliation, and the single-stranded DNA was immobilized onto it. Under optimal conditions, the peak current of the differential pulse voltammetry method exhibited a linear relationship with the logarithm of the concentration of target-complementary-stranded DNA, ranging from 1.0 × 10-15 to 1.0 × 10-11 M, with a detection limit of 3.46 × 10-16 M. The topological material Bi2Se3, with Dirac surface states, enhanced the signal-to-interference plus noise ratio of the electrochemical measurements, thereby improving the sensitivity of the sensor. Furthermore, the electrochemical sensor demonstrated excellent specificity in recognizing RNA. It can detect complementary RNA by amplifying and transcribing the initial DNA template, with an initial DNA template concentration ranging from 1.0 × 10-18 to 1.0 × 10-15 M. Furthermore, the sensor also effectively distinguished negative and positive results by detecting splitting-synthetic SARS-CoV-2 pseudovirus with a concentration of 1 copy/µL input. Our work underscores the immense potential of the electrochemical sensing platform based on the topological material Bi2Se3 in the detection of pathogens during the rapid spread of acute infectious diseases.

Integrated biosensor array for multiplex biomarkers cancer diagnosis via in-situ self-assembly carbon nanotubes with an ordered inverse-opal structure.

To enhance the precision and reliability of early disease detection, especially in malignancies, an exhaustive investigation of multi-target biomarkers is essential. In this study, an advanced integrated electrochemical biosensor array that demonstrates exceptional performance was constructed. This biosensor was developed through a controllable porous-size mechanism and in-situ modification of carbon nanotubes (CNTs) to quantify multiplex biomarkers-specifically, C-reaction protein (CRP), carbohydrate antigen 125 (CA125), and carcinoembryonic antigen (CEA)-in human serum plasma. The fabrication process involved creating a highly ordered three-dimensional inverse-opal structure with the CNTs (pCNTs) modifier through microdroplet-based microfluidics, confined spatial self-assembly of nanoparticles, and chemical wet-etching. This innovative approach allowed for direct in-situ modification of nanomaterial onto the surface of electrode array, eliminating secondary transfer and providing exceptional control over structure and stability. The outstanding electrochemical performance was achieved through the synergistic effect of the pCNTs nanomaterial, aptamer, and horseradish peroxidase-labeled (HRP-) antibody. Additionally, the integrated biosensor array platform comprised multiple individually addressable electrode units (n = 11), enabling simultaneous multi-parallel/target testing, thereby ensuring accuracy and high throughput. Crucially, this integrated biosensor array accurately quantified multiplex biomarkers in human serum, yielding results comparable to commercial methods. This integrated technology holds promise for point-of-care testing (POCT) in early disease diagnosis and biological analysis.

Highly catalytic sulfur-doped and bimetal-coordinated CoFe(CN)5NO nanoparticles coupled with PER/HCR amplification cascades for sensitive electrochemical aptamer luteinizing hormone assay.

Sensitive monitoring of luteinizing hormone (LH), a glycoprotein that regulates the synthesis of regulatory steroid hormones, can facilitate the diagnosis of various reproductive diseases. In this work, a new and highly catalytic Sulfur-doped and bimetal-coordinated CoFe(CN)5NO (denoted as S-CoFe(CN)5NO) nanoparticles are synthesized. Such material is further used to construct high performance sensing interface and coupled with primer exchange reaction (PER) and hybridization chain reaction (HCR) amplification cascades for sensitive electrochemical aptamer-based LH assay. Target LH molecules bind aptamer sequences in DNA duplex probes to liberate ssDNA strands, which initiate subsequent PER/HCR amplification cascades for the capture of many ferrocene (Fc)-tagged DNAs on sensing interface. S-CoFe(CN)5NO subsequently leads to catalytic oxidation of these Fc tags for yielding substantially magnified currents for realizing ultrasensitive assay of LH with the detection limit of 0.69 pM in range from 5 pM to 10 nM. Owing to the high specificity of aptamer, such sensor has high selectivity and can achieve low levels of LH assay in diluted serum samples. With the successful demonstration for detecting trace LH, such sensor can be easily extended as a universal aptamer-based electrochemical sensing method for monitoring various target analytes in the biomedical and biological fields.

Smartphone-enabled flow injection amperometric glucose monitoring based on a screen-printed carbon electrode modified with PEDOT@PB and a GOx@PPtNPs@MWCNTs nanocomposite.

This study presents a modified screen-printed carbon electrode (SPCE) to determine glucose in a custom-built flow injection system. The biosensor was constructed by immobilizing glucose oxidase on porous platinum nanoparticles decorated on multi-walled carbon nanotubes (GOx@PPtNPs@MWCTNs). The fabrication of the biosensor was completed by coating the GOx@PPtNPs@MWCTNs nanocomposite on an SPCE modified with a nanocomposite of poly(3,4-ethylenedioxythiophene) and Prussian blue (GOx@PPtNPs@MWCTNs/PEDOT@PB/SPCE). The fabricated electrode accurately measured hydrogen peroxide (H2O2), the byproduct of the GOx-catalyzed oxidation of glucose, and was then applied as a glucose biosensor. The glucose response was amperometrically determined from the PB-mediated reduction of H2O2 at an applied potential of -0.10 V in a flow injection system. Under optimal conditions, the developed biosensor produced a linear range from 2.50 µM to 1.250 mM, a limit of detection of 2.50 µM, operational stability over 500 sample injections, and good selectivity. The proposed biosensor determined glucose in human plasma samples, achieving recoveries and results that agreed with the hexokinase-spectrophotometric method (P > 0.05). Combining the proposed biosensor with the custom-built sample feed, a portable potentiostat and a smartphone, enabled on-site glucose monitoring.

Target-promoted autocatalytic hairpin assembly of bivalent DNAzymes for sensitive and label-free electrochemical metallothionein assay.

Metallothionein (MT) has shown to be an important biomarker for environmental monitoring and various diseases, due to its significant binding ability to heavy metal ions. On the basis of such a characteristic and the Hg2+-stabilized DNA duplex (Hg2+-dsDNA) probe, as well as a new autocatalytic hairpin assembly (aCHA)/DNAzyme cascaded signal enhancement strategy, the construction of a highly sensitive and label-free electrochemical MT biosensor is described. Target MT molecules bind Hg2+ in Hg2+-dsDNA to disrupt the duplex structure and to release ssDNA sequences, which trigger subsequent aCHA for efficient production of mimic aCHA triggering strands and many bivalent DNAzymes. The signal hairpins on the electrode are then cyclically cleaved by DNAzyme amplification cascade to liberate plenty G-quadruplex sequences, which bind hemin and yield largely enhanced currents for sensitive assay of MT with a detection limit of 0.217 nM in a label-free approach. Such sensor also shows selective discrimination capability to MT against other interfering proteins and assay of MT in normal serums with dilution has also been verified, indicating its potential for highly sensitive detection of different heavy metal ion binding molecules for various application scenarios.