Linear Detection Range Research Articles

A novel fluorescence sensor based on Al3+-mediated aggregation of gold nanoclusters for determination of citric acid in beverages.

This paper revealed a new strategy for citric acid (CA) detection using aggregation-induced emission (AIE)-based fluorescent gold nanoclusters (AuNCs). AuNCs was synthesized using glutathione (GSH) as the template and reducing agent and used as the fluorescent probe to detect CA under aluminum ion (Al3+) mediation. The fluorescence intensity of AuNCs increased about 4 times with the addition of Al3+, but the enhanced fluorescence was quenched after the addition of CA. Based on this fluorescence phenomenon, an "on-off" fluorescence strategy was designed for the sensitive determination of CA and a linear detection range for CA was achieved within 0-80.0 μM. In addition, the developed probe exhibited high selectivity and accuracy for determination of CA. The mechanism of fluorescence enhancement and quenching of AuNCs was explored in detail. The established probe was used successfully for CA detection in beverages. The spiked recoveries from 97.50% to 103.67% were gratifying, which indicated the probe had potential prospects for detecting CA in food.

A novel low oxidation potential hydroxyurea sensor utilizing flower-shaped Zn and N co-doped porous carbon coupled with graphene oxide via one-step electrodeposition

Accurate monitoring of hydroxyurea (HU) dosage is imperative in the administration of anticancer drugs. Existing determination methods face challenges such as operational complexity, low sensitivity, or high oxidation potentials. In this study, a novel HU electrochemical sensor (Zn/N-PC/GO/GCE) was synthesized using flower-shaped Zn/N co-doped porous carbon (Zn/N-PC) with graphene oxide (GO) through a one-step electrodeposition. The sensor features a distinctive three-step oxidation process for HU with a low oxidation potential, attributed to an electrochemical activation electrode strategy and crucial Zn/N co-doping in Zn/N-PC. Three electrons involved oxidation process of HU and Zn/N-PC/GO adsorption energy through transferred electrons and density functional theory (DFT). Under optimized conditions, the sensor demonstrated a broad linear detection range (1–1000 μM) and an impressive limit of detection (LOD) of 0.52 μM. Applicability was confirmed by analyzing HU in tablet formulations, urine and serum samples. This study presents an innovative electrochemical method for accurate HU monitoring, elucidating a potential three-step oxidation mechanism.

RuSe2/CuO nanohybrids coupled with ALP-assisted for MMP-9 photoelectrochemical assay

A photoelectrochemical (PEC) assay strategy for the detection of matrix metalloproteinase-9 (MMP-9) was fabricated. RuSe2/CuO nanohybrids were first prepared by hydrothermal method. As a transition metal element semiconductor, RuSe2 has excellent optical and electrical properties. By combining the excellent conductivity and adjustable bandgap of CuO, a binary heterojunction nanoflower with high photoelectric response was obtained. The combination of RuSe2 and CuO reduces the electron hole recombination rate; the RuSe2/CuO nanohybrids exhibits a higher photocurrent response. In the MMP-9 PEC strategy determination, the magnetic beads (MB)-peptide-alkaline phosphatase (ALP) recognition probe was formed by modifying C-terminal of the peptide chain with biotin and binding to ALP, and the N-terminal was connected to carboxylated MB. When the target MMP-9 exists, the recognition probe, MB-Peptide-ALP, was recognized by MMP-9 to cut the substrate area and coding area and release ALP, catalyzing the hydrolysis of O-phosphonoxyphenol (OPP) to produce benzene-1,2-diol in situ, the photocurrent response was generated. This strategy provides lower background PEC noise for detecting MMP-9, with the advantage of simplicity and the sensitivity than conventional ELISA. The results showed that the recognition peptide probe PEC method achieved ultra-high sensitivity detection of target MMP-9, with a linear detection range of 1 pg/mL–100 ng/mL and a detection limit of 0.3 pg/mL (S/N = 3). The results of PEC assay strategy in human serum sample give the recoveries rate of 94.3 % to 108.1 % and relative standard deviation of 0.45–5.87 %.

The investigation of the interaction between fluorescent carbon dots labeling silk fibroin using a fluorescence microscope–surface plasmon resonance system

The use of fluorescent carbon dots (CDs) as highly precise biolabeling probes has been widespread in the fields of live cell imaging and protein labeling due to their small size and excellent photoluminescence ability to accurately target specific molecules with surface chemical properties. However, there was a lack of research on the interaction between CDs and labeled molecules. In this work, we presented a novel investigation strategy, the fluorescence microscopy-surface plasmon resonance (FM-SPR) system, which combined the use of fluorescence microscopy and wavelength modulation surface plasmon resonance to study the interaction between CDs and labeled molecules in real-time. Using this system, simultaneously recorded the SPR signals and the fluorescence images on the surface of the FM-SPR sensor chip. We observed the dynamic curve and fluorescence images of the interaction between green emissive nitrogen-doped carbon dots (N-CDs) and silk fibroin (SF) in real-time. The kinetic parameters, the quantitative analysis, and the investigation of the binding could be achieved. The results showed a strong linear relationship between the change in SPR signals and the concentration of N-CDs, with a linear coefficient of 0.99913. The linear detection range was 2.5 μg/mL–100 μg/mL, and the real lowest detection limit reached 0.5 μg/mL. Additionally, the green fluorescence points in the imaging region on the FM-SPR sensor chip increased with the concentration of N-CDs, which was consistent with the change in SPR signals. Using this system we also acquired the association rate and dissociation rate of N-CDs to SF which were 2.65 × 10−5/s and 1.52 × 10−5/s, respectively. This demonstrated the effectiveness of our method in quantitatively analyzing SF labeled with N-CDs.

Development of transcriptional factor-based whole-cell biosensors to monitor and degrade antibiotics using mutant cells obtained via adaptive laboratory evolution

With the widespread use of antibiotics and increasing environmental concerns regarding antibiotic abuse, the detection and degradation of antibiotic residues in various samples has become a pressing issue. Transcriptional factor (TF)-based whole-cell biosensors are low-cost, easy-to-use, and flexible tools for detecting chemicals and controlling bioprocesses. However, because of cytotoxicity caused by antibiotics, the application of such biosensors is limited in the presence of antibiotics. In this study, we used antibiotic-tolerant mutants obtained via adaptive laboratory evolution (ALE) to develop TF-based whole-cell biosensors for antibiotic monitoring and degradation. The biosensors had high performance and stability in detecting relatively high concentrations of tetracycline (Tc) and nisin. The ALE mutant-based Tc biosensor exhibited a 10-fold larger linear detection range than the wild-type strain-based biosensor. Then, the Tc biosensor was employed to detect residual amounts of Tc in mouse stool, serum, and urine samples and facilitate Tc biodegradation in mouse stool, demonstrating its high utility. Considering that ALE has been demonstrated to enhance cell tolerance to various toxic chemicals, our strategy might facilitate the development of whole-cell biosensors for most antibiotics and other toxic ligands.

Ultrasensitive detection of chlortetracycline in animal-origin food using molecularly imprinted electrochemical sensor based on SnS2/ZnCo-MOF and AuNPs

The chlortetracycline (CTC) residue in food poses a threat to human health. Therefore, developing sensitive, convenient and selective analytical methods for CTC detection is crucial. This study innovatively uses tin disulfide/bimetallic organic framework (SnS2/ZnCo-MOF) nanocomposites in conjunction with gold nanoparticles (AuNPs) to co-modify a glassy carbon electrode (GCE). Further, a molecularly imprinted polymer (MIP)-based electrochemical sensing platform Au-MIP/SnS2/ZnCo-MOF/Au/GCE (AZG) was fabricated for selective CTC detection. SnS2/ZnCo-MOF enhanced the stability and surface area of the AZG sensor. The presence of AuNPs facilitated electron transport between the probe and the electrode across the insulating MIP layer. The fixation of AuNPs and MIP via electropolymerization enhanced the selective recognition of this sensor and amplified its output signal. The AZG sensor demonstrated a wide linear detection range (0.1–100 μM), low detection limit (0.072 nM), and high sensitivity (0.830 μA μM−1). It has been used for detecting CTC in animal-origin food with good recovery (96.08%–104.60%).

MOF-derived yolk-shell CoN/Co-NC@SiO2 nanozyme with oxidase mimetic activities for colorimetric detection of glutathione

The development of nanozymes has garnered significant attention in biosensing applications owing to their exceptional catalytic properties and structural tunability. Herein, we present a yolk-shell nanozyme derived from metal-organic frameworks (MOFs) featuring CoN/Co-NC@SiO2 architecture, exhibiting remarkable oxidase mimetic activities for colorimetric glutathione (GSH) detection. The synthesis involves a facile pyrolysis process of cobalt-based MOFs encapsulated within a silica shell, resulting in a unique yolk-shell nanostructure with CoN/Co-NC active sites. Yolk-shell CoN/Co-NC@SiO2 has been studied in detail as an oxidase and catalase-like nanozyme. In consideration of structural and composition modulation, including hydrophilic SiO2 shell, the unique cavity, a high specific surface area and dispersed active sites, the CoN/Co-NC@SiO2 was proposed for colorimetric detection of glutathione with its oxidase-like activities. Based on the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) by CoN/Co-NC@SiO2, a wide linear detection range of 0.5–60 μM as well as a lower detection limit of 0.054 μM were obtained. Our research shows that optimizing structure and composition plays an important role in the construction of multiple-enzyme activity and offers bright potential applications of MOF-derived yolk-shell nanozymes in biosensing and medical diagnostics.

Gold nanoparticles-doped MXene heterostructure for ultrasensitive electrochemical detection of fumonisin B1 and ampicillin.

Early transition metal carbides (MXene) hybridized by precious metals open a door for innovative electrochemical biosensing device design. Herein, we present a facile one-pot synthesis of gold nanoparticles (AuNPs)-doped two-dimensional (2D) titanium carbide MXene nanoflakes (Ti3C2Tx/Au). Ti3C2Tx MXene exhibits high electrical conductivity and yields synergistic signal amplification in conjunction with AuNPs leading to excellent electrochemical performance. Thus Ti3C2Tx/Au hybrid nanostructure can be used as an electrode platform for the electrochemical analysis of various targets. We used screen-printed electrodes modified with the Ti3C2Tx/Au electrode and functionalized with different biorecognition elements to detect and quantify an antibiotic, ampicillin (AMP), and a mycotoxin, fumonisin B1 (FB1). The ultralow limits of detection of 2.284pM and 1.617pg.mL-1, which we achieved respectively for AMP and FB1 are far lower than their corresponding maximum residue limits of 2.8nM in milk and 2 to 4mgkg-1 in corn products for human consumption set by the United States Food and Drug Administration. Additionally, the linear range of detection and quantification of AMP and FB1 were, respectively, 10pM to 500nM and 10pgmL-1 to 1µgmL-1. The unique structure and excellent electrochemical performance of Ti3C2Tx/Au nanocomposite suggest that it is highly suitable for anchoring biorecognition entities such as antibodies and oligonucleotides for monitoring various deleterious contaminants in agri-food products.

Iodine-doped reduced graphene oxide and titanium dioxide nanocomposite as effective amperometric glucose biosensor

The current study fabricated a non-enzymatic glucose sensor based on iodine-doped reduced graphene oxide with titanium dioxide (I-rGO@TiO2) nanocomposite. Initially, the sol-gel and thermal reduction methods synthesized titanium dioxide (TiO2) nanoparticles and reduced graphene oxide (rGO). Then, the hydrothermal technique was utilized to synthesize a composite of I-rGO@TiO2 by combining I-rGO and TiO2 in a 1:4 ratio. The XRD spectrum and TEM images revealed that in the I-rGO@TiO2 nanocomposite, nanocrystalline anatase titanium is randomly distributed on the I-rGO sheets. Fourier transforms the infrared spectrum of nanocomposite shows the presence of titanium and oxygen bond characteristics peak between 400 and 850 cm−1. Iodine molecules peak at 100 cm−1 were obtained in Raman spectra. The AC conductivity and dielectric properties of the nanocomposite were analyzed. For the sensor fabrication, the indium tin oxide electrode surface is modified by I-rGO@TiO2, and the electrochemical performance was examined. At room temperature, the sensor demonstrated a wider linear detection range (0.5−10 mM). The lower detection limit of the sensor was 0.23 μM (S/N = 3), and the sensitivity was 221.69 μA mM−1 cm−2. The I-rGO@TiO2 nanocomposite shows a positive temperature coefficient via the thermal activation of charge carriers and a conductivity of 3.82 × 10−5 Ω−1m−1 at 200 °C. Additionally, the antibacterial properties was evaluated, and dose-dependent properties were observed towards E. coli and Bacillus subtilis bacterium.

Tube-Like Copper Cobalt Oxide Anchored with Multiwalled Carbon Nanotube Nanocomposite Modified Glassy Carbon Electrode for the Electrochemical Detection of Nilutamide

Developing a precise and effective method to detect Nilutamide (NIL) is essential due to its contamination of the environment, which poses significant risks to human health and the biosphere. In this study, we employed a simple hydrothermal technique to create a nanocomposite of CuCo2O4 (copper cobalt oxide) and multi-walled carbon nanotube (MWCNT), which was then anchored onto a glassy carbon electrode for NIL detection. Various spectroscopic techniques were employed to confirm the structure of the nanomaterial, and its electrochemical properties were examined using cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy. The CuCo2O4/MWCNT nanocomposite-modified electrode exhibited a wide linear detection range from 0.01 to 170 μM, a high sensitivity of 1.50 μA μM−1 cm−2, a low detection limit of 0.01 μM, outstanding stability, repeatability, and practical applicability for NIL detection.

3D porous conductive matrix based on phase-transited BSA and covalent coupling-stabilized transition ZnS-CNT for antifouling and on-site detection of nitrite in soil

Nitrite plays a critical role in a variety of nitrification and denitrification processes in the nitrogen cycle. Due to the high surface energy, tendency to aggregate, and poor conductivity, current nitrite ZnS-based sensing platform could not meet the need of on-site nitrite detection in smart agriculture. In order to address these issues, the carboxylated carbon nanotube (CNT) was introduced to reduce the surface energy and prevented aggregation of ZnS, while ZnS-carboxylated CNT (ZnS-CNT) composite also provided excellent electrochemical conductivity. Furthermore, the introduction of phase transition BSA (PTB) created a three-dimensional porous conductive matrix without interfering with the mass transfer process of nitrite. The resulting sensing platform exhibited a linear detection range of 10 nM to 0.4 mM for nitrite, with a detection limit of 0.73 nM. And this sensing platform had the excellent antifouling ability to direct detection nitrite in real soil suspension. In addition, the sensing platform demonstrated remarkable resistance to interferences from pH variations, microbial presence, and organic pollutants that usually present in soil environment. Therefore, on-site detection of nitrite ions in soil environment was realized no needing complex pretreatments.

CuO nanoparticles passivated 2D MXene-based voltammetric sensor for detecting environmental hazardous pollutant

This research explores a novel method for electrochemical sensing of the organic pollutant diclofenac sodium. Glassy carbon electrodes (GCEs) were modified with ultrasonically prepared MXene/CuO nanoparticle composites, demonstrating a wide linear detection range of 0.34 µM–31.67 µM for the contaminant. The study involved synthesizing 2D MXene via HF etching and DMSO delamination, and CuO nanoparticles through a hydrothermal process. Powder XRD, FE-SEM, EDAX, HR-TEM, and SAED techniques characterized the synthesized materials and composites. Cyclic voltammetry (CV), differential pulse voltammetry (DPV), square wave voltammetry (SWV), and electrochemical impedance spectroscopy (EIS) were employed to analyze the electrochemical behaviour of the nanocomposites. Furthermore, the binding interaction between the MXene/CuO composite and diclofenac sodium was investigated using molecular modelling and semi-empirical approaches. The results revealed that CuO nanoparticle incorporation significantly enhances the sensitivity of MXene towards diclofenac. This novel sensor exhibited satisfactory performance, suggesting its potential application as a robust platform for environmental monitoring systems.

Cytosine-Rich Oligonucleotide and Electrochemically Reduced Graphene Oxide Nanocomposite for Ultrasensitive Electrochemical Ag+ Sensing.

Silver ions (Ag+) are crucial in various fields, but pose environmental and health risks at high concentrations. This study presents a straightforward approach for the ultra-trace detection of Ag+, utilizing a composite of a cytosine-rich oligonucleotide (CRO) and an electrochemically reduced graphene oxide (ERGO). Initially, ERGO was synthesized on a glassy carbon electrode (GCE) through the reduction of graphene oxide (GO) via cyclic voltammetry. A methylene blue-tagged CRO (MB-CRO) was then anchored to the ERGO surface through π-π interactions, resulting in the formation of an MB-CRO-modified ERGO electrode (MB-CRO/ERGO-GCE). The interaction with Ag+ ions induced the formation of silver-mediated C-Ag+-C coordination, prompting the MB-CRO to adopt a hairpin structure. This conformational change led to the desorption of the MB-CRO from the ERGO-GCE, causing a variation in the redox current of the methylene blue associated with the MB-CRO. Electrochemical assays revealed that the sensor exhibits extraordinary sensitivity to Ag+ ions, with a linear detection range from 1 femtomolar (fM) to 100 nanomolars (nM) and a detection limit of 0.83 fM. Moreover, the sensor demonstrated high selectivity for Ag+ ions and several other benefits, including stability, reproducibility, and straightforward fabrication and operational procedures. Additionally, real sample analyses were performed using the modified electrode to detect Ag+ in tap and pond water samples, yielding satisfactory recovery rates.

Electrochemical Non-Enzymatic Glucose Sensing Platform Based on Vanadium Pentoxide Film-Modified Screen Printed Gold Electrode

A screen printed gold electrode (SPGE) served as the foundation for directly depositing Vanadium pentoxide (V2O5), crafting an enzyme-free glucose sensor. Through cyclic voltammetry in an alkaline setting, the sensor's ability to drive glucose oxidation was explored. Utilizing V2O5 as an electrocatalyst, this non-enzymatic sensor exhibited an expansive linear detection range (1 mM–10 mM) and an impressively low detection limit of 0.9 μM. These results underscored V2O5's robust electrocatalytic process in facilitating glucose oxidation within alkaline solutions, unaffected notably by substances like ascorbic acid, fructose and maltose. This investigation highlights a direct and efficient method for glucose detection without reliance on enzymes.

Potential powered EC-SERS for sensitive detection of acetamiprid

Surface-enhanced Raman spectroscopy (SERS) is a powerful tool for rapid and sensitive detection of pesticide residues in food, and the applied potential regulated SERS technique can be endowed with a higher sensitivity. In this work, we developed an electrochemical-surface enhanced Raman spectroscopy (EC-SERS) sensor for the rapid detection of acetamiprid (AAP) in vegetables. AuNPs/ITO were prepared via in-situ electrodeposition of gold nanoparticles (AuNPs) on an indium tin oxide (ITO) both as a SERS substrate and working electrode. By adding AAP into an in-situ Raman electrolytic cell with an applied electrochemical potential (+0.3 V), the SERS intensity was enhanced by 4-fold and the characteristic signal was linearly related to the concentration of AAP. Under the optimal conditions, the EC-SERS method exhibited a linear detection range from 0.05 to 50 μM, with a limit of detection (LOD, 3S/M) of 0.02 μM. Simultaneously, based on density functional theory (DFT), the adsorption characteristics of AAP on AuNPs/ITO were studied in the presence of electric field. The method was finally confirmed by HPLC-MS for the detection of real samples, revealing its potential application in food safety.

Development of a biophotonic fiber sensor using direct-taper and anti-taper techniques with seven-core and four-core fiber for the detection of doxorubicin in cancer treatment

Doxorubicin (DOX) is an important drug for cancer treatment, but its clinical application is limited due to its toxicity and side effects. Therefore, detecting the concentration of DOX during treatment is crucial for enhancing efficacy and reducing side effects. In this study, the authors developed a biophotonic fiber sensor based on localized surface plasmon resonance (LSPR) with the multimode fiber (MMF)-four core fiber (FCF)-seven core fiber (SCF)-MMF-based direct-taper and anti-taper structures for the specific detection of DOX. Compared to other detection methods, it has the advantages of high sensitivity, low cost, and strong anti-interference ability. In this experiment, multi-walled carbon nanotubes (MWCNTs), cerium-oxide nanorods (CeO2-NRs), and gold nanoparticles (AuNPs) were immobilized on the probe surface to enhance the sensor's biocompatibility. MWCNTs and CeO2-NRs provided more binding sites for the fixation of AuNPs. By immobilizing AuNPs on the surface, the LSPR was stimulated by the evanescent field to detect DOX. The sensor surface was functionalized with DOX aptamers for specific detection, enhancing its specificity. The experiments demonstrated that within a linear detection range of 0-10 µM, the sensitivity of the sensor is 0.77 nm/µM, and the limit of detection (LoD) is 0.42 µM. Additionally, the probe's repeatability, reproducibility, stability, and selectivity were evaluated, indicating that the probe has high potential for detecting DOX during cancer treatment.

Enzyme-integrated metal-organic framework platform for cascade detection of α-amylase

As one of the most important industrial enzymes, α-amylase is widely used in food processing, such as starch sugar and fermentation, bringing high added value to industry of more than a trillion dollars. We developed a multi-enzyme system (Glu&Gox@Cu-MOF-74) prepared by embedding α-glucosidase (Glu) and glucose oxidase (Gox) into the biomimetic metal-organic framework Cu-MOF-74 using in situ encapsulation within 15 min at room temperature for efficient and sensitive detection of α-amylase activity. Benefitting from the remarkable peroxidase-mimicking property and rigid skeleton of Cu-MOF-74, the biocatalytic platform exhibited excellent cascade activity and tolerance in various extremely harsh environments compared to natural enzymes. On this basis, a cascade biocatalytic platform was constructed for the detection of α-amylase activity with wide linear range (5–100 U/L) and low limit of detection (1.45 U/L). The colorimetric cascade scheme is important for the sensitive and selective determination of α-amylase in complex fermentation samples, and the detection time is short (∼0.5 h). This work provides new ideas for the detection of α-amylase based on the cascade amplification method.

Optical Fiber Surface Plasmon Resonance Sensor for Glyceryl Tributyrate Detection Based on the PAA/CS Composite Hydrogel Embedding Protease Method.

Glycerol tributyrate as a low-density lipoprotein plays a crucial role in drug development and food safety. In this work, a novel high-stability fiber optic sensor for glyceryl tributyrate based on the poly(acrylic acid) (PAA) and chitosan (CS) composite hydrogel embedding method is first proposed. Compared with traditional functionalization, the lipase in a polymer network structure used in this article can not only avoid chemical reactions that cause damage to the enzyme structure but also avoid the instability of ionic bonds and physical adsorption. Therefore, the PAA/CS hydrogel method proposed in this article can effectively retain enzyme structure. First, the impact of different layers (one to five layers) of PAA/CS on pH sensing performance was explored, and it was determined that layers 1-3 could be used for subsequent sensing experiments. Within the linear detection range of 0.5-10 mM, the detection sensitivities of the one to three layers of the biosensor are divided into 0.65, 0.95, and 1.51 nm/mM, respectively, with the three layers having the best effect. When the number of coating layers is three, the detection limit of the sensor is 0.47 mM, meeting the millimole level detection standard for anticancer requirement. Furthermore, the stability and selectivity of the sensor (in the presence of hemoglobin, urea, cholesterol, acetylcholine, and glucose) were analyzed. The three-layer sensor is used for sample detection. At concentrations of 1-10 mM, the absolute value of the recovery percentage (%) is 82-99%, which can accurately detect samples. The sensor proposed in this paper has the advantages of low sample consumption, high sensitivity, simple structure, and label-free measurement. The enzyme-embedding method provides a new route for rapid and reliable glyceryl tributyrate detection, which has potential applications in food safety as well as the development of anticancer drugs.

N/S co-doped carbon dots-based solution-gated graphene transistors (SGGT) for ultra-sensitive and selective determination of Hg (II) ions in real water and serum samples

The conventional methods for detecting Hg2+ ions are generally impaired by low sensitivity, a high limit of detection (LOD), and the long detection time required. In this work, we develop a novel solution gated graphene transistor (SGGT) based on carbon dots doped with N and S elements (N/S CDs) as gate electrode probes. The prepared N/S CDs, which are 3–5 nm in diameter, are first modified at the gate of the SGGT through covalent bonding that specifically recognizes Hg2+ ions. The SGGT is then used as a Hg2+ sensor, exhibiting good selectivity, ultrahigh sensitivity, good reproducibility, and a short detection time. The SGGT sensor has an excellent linear detection range, from 0.1 fM to 1 nM. The LOD can reach 28 aM, which is far lower than that of conventional detection methods. Moreover, the SGGT sensor also has a rapid response time of ∼ 40 s. Finally, the ability to analyze real water samples and serum samples is demonstrated.

High-density aptamer synthesis based on primer exchange reaction for label-free electrochemical biosensing

We report an electrochemical aptamer-based (E-AB) sensor for label-free quantitative detection of thrombin. In-situ synthesis of high-density aptamer replicas on the electrode is accomplished based on primer exchange reaction (PER), by which a DNA primer is continuously extended with the presence of a catalytic hairpin template and DNA polymerase. The PER enables the synthesis of long single-stranded DNA with replicated aptamer sequence for thrombin binding. The PER products on the surface of a gold electrode increase the density of aptamers on a limited electrode area, which can provide more effective binding sites for thrombin and therefore improve the performance of the sensor based on electrochemical impedance spectroscopy. Compared with the conventional E-AB sensor based on a 15-mer aptamer immobilized on the electrode, our method has a lower detection limit of 0.91 pM, and a wider linear range of 1.0 pM to 50 nM. Therefore, we believe our method is promising for label-free electrochemical detection of biomarkers.