Additional file 1: Figure S1. of Streptavidin Modified ZnO Film Bulk Acoustic Resonator for Detection of Tumor Marker Mucin 1

SEM images after every step of the reaction: (a) streptavidin self-assembly on the FBAR on FBAR, (b) the prepared AuNPs-MUC1 ampters chelates, (c) few AuNPs-MUC1 ampters chelates captured by streptavidin without target MUC1, and (d) a large amount of AuNPs-MUC1 ampters chelates captured by streptavidin with target MUC1. (JPG 60 kb

Ultrasensitive Electrochemical Biosensor for HIV Gene Detection Based on Graphene Stabilized Gold Nanoclusters with Exonuclease Amplification

Because human immunodeficiency virus (HIV) has been one of the most terrible viruses in recent decades, early diagnosis of the HIV gene is of great importance for all scientists around the world. In our work, we developed a novel electrochemical biosensor based on one-step ultrasonic synthesized graphene stabilized gold nanocluster (GR/AuNC) modified glassy carbon electrode (GCE) with an exonuclease III (Exo III)-assisted target recycling amplification strategy for the detection of HIV DNA. It is the first time that GR/AuNCs have been used as biosensor platform and aptamer with cytosine-rich base set as capture probe to construct the biosensor. With the combination of cytosine-rich capture probe, good conductivity and high surfaces of GR/AuNCs, and Exo III-assisted target recycling amplification, we realized high sensitivity and good selectivity detection of target HIV DNA with a detection limit of 30 aM (S/N = 3). Furthermore, the proposed biosensor has a promising potential application for target detection in human serum analysis

Metal-Mediated Polydopamine Nanoparticles–DNA Nanomachine Coupling Electrochemical Conversion of Metal–Organic Frameworks for Ultrasensitive MicroRNA Sensing

The development of a robust sensing platform with an efficient probe assembly, and ingenious signal conversion is of great significance for bioanalytical application. In this work, a multipedal polydopamine nanoparticles–DNA (PDANs-DNA) nanomachine coupling electrochemical-driven metal–organic frameworks (MOFs) conversion-enabled biosensing platform was constructed. The PDANs-DNA nanomachine was designed based on Ca2+-mediated DNA adsorption and target-triggered catalytic hairpin assembly on PDANs, which not only maintained the DNA immobilization simplicity but also possessed a high walking efficiency. PDANs-DNA nanomachine could walk fast on the electrode via multiple legs under exonuclease III driving, resulting in the formation of DNA dendrimers through two hairpins assembly. The MOFs (Fe-MIL-88-NH2) probe was decorated on the DNA dendrimers to act as a porous metal precursor and converted into electroactive Prussian Blue by a controlled electrochemical approach, which was a facile, simple, and room-temperature approach compared with the commonly employed MOFs conversion methods. Using microRNA-21 (miRNA-21) as the model target, the proposed biosensor achieved miRNA-21 detection ranging from 10 aM to 10 pM with the detection limit of 5.8 aM. The proposed strategy presented a highly efficient walking platform with the ingenious electrochemical conversion of MOFs, providing more options for the design of an electrochemical platform and holding potential applications in clinical analysis and disease diagnosis

Enhanced Single-Particle Collision Electrochemistry at Polysulfide-Functionalized Microelectrodes for SARS-CoV‑2 Detection

Single-particle collision electrochemistry (SPCE) has shown great promise in biosensing applications due to its high sensitivity, high flux, and fast response. However, a low effective collision frequency and a large number of interfering substances in complex matrices limit its broad application in clinical samples. Herein, a novel and universal SPCE biosensor was proposed to realize sensitive detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) based on the collision and oxidation of single silver nanoparticles (Ag NPs) on polysulfide-functionalized gold ultramicroelectrodes (Ps-Au UMEs). Taking advantage of the strong interaction of the Ag–S bond, collision and oxidation of Ag NPs on the Ps-Au UME surface could be greatly promoted to generate enhanced Faraday currents. Compared with bare Au UMEs, the collision frequency of Ps-Au UMEs was increased by 15-fold, which vastly improved the detection sensitivity and practicability of SPCE in biosensing. By combining magnetic separation, liposome encapsulation release, and DNAzyme-assisted signal amplification, the SPCE biosensor provided a dynamic range of 5 orders of magnitude for spike proteins with a detection limit of 6.78 fg/mL and a detection limit of 21 TCID50/mL for SARS-CoV-2. Furthermore, SARS-CoV-2 detection in nasopharyngeal swab samples of infected patients was successfully conducted, indicating the potential of the SPCE biosensor for use in clinically relevant diagnosis

Visual Discrimination of Phenolic Group β₂‑Agonists and the Ultrasensitive Identification of Their Oxidation Products by Use of a Tyrosinase-Based Catalytic Reaction

The fast, visual discrimination of β2-agonist drugs is needed for the on-site screening of various types of β2-agonists in blood and urine samples. We developed a simple, rapid, one-step colorimetric method to detect phenolic β2-agonists by use of a tyrosinase catalytic reaction, which involved the oxidation of the phenol group on the benzene rings of β2-agonists. The enzymatic oxidation products of β2-agonists with phenolic groups exhibited different color transitions based on the different substituent groups on the aromatic ring, whereas β2-agonists with the aniline group or the resorcinol group remained colorless. This visual color discrepancy has been used to intuitively and conveniently differentiate the phenolic group β2-agonists, such as ractopamine, isoxsuprine, ritodrine, and fenoterol. The oxidation products of these compounds have been identified using mass spectrometry, and the possible reaction mechanisms between β2-agonists and tyrosinase have been deduced. The parameters that govern the analytical performance of the reaction product, including the pH of the buffer solution, the concentration of tyrosinase, and the incubation time, have been studied and optimized using ultraviolet–visible (UV–vis) spectroscopy and electrochemical methods. Under the optimal experimental conditions, the absorbance intensity and electrochemical signal were found to increase proportionally to the concentrations of the phenolic group β2-agonists, which gave a quantitative description of the β2-agonists in solution

In Situ Measurement of ATP in Single Cells by an Amphiphilic Aptamer-Assisted Electrochemical Nano-Biosensor

In situ and quantitative measurements of adenosine 5′-triphosphate (ATP) in single living cells are highly desired for understanding several sorts of necessary physiological and pathological processes. Due to its small size and high sensitivity, an ultra-microelectrode can be used for single-cell analysis. However, ATP is difficult to detect in single cells because it is nonelectroactive and low in content. Herein, we introduced an electrochemical nano-biosensor based on an amphiphilic aptamer-assisted carbon fiber nanoelectrode (aptCFNE) with high signal-to-noise ratio. The low current (e.g., 60 pA) and the tiny diameter of the tip (ca. 400 nm) of the nanosensor made it noninvasive to living cells. The amphiphilic aptamer has good biocompatibility and can be stably modified to the surface of functionalized electrodes. CFNE, which was modified with ferrocene-labeled aptamer, could quickly and selectively detect ATP content in the nucleus, cytoplasm, and extracellular space of single HeLa cells. The results showed that the ATP contents in the nucleus, cytoplasm, and extracellular space were 568 ± 9, 461 ± 20, and 312 ± 4 μM, respectively. The anticancer drug treatment effects on the cellular level were further recorded, which was of great significance for understanding ATP-related biological processes and drug screenings. This strategy is universally applicable to detect other targets by changing the aptamer sequence, which will greatly improve our understanding of cell heterogeneity and provide a more reliable scientific basis for exploring major diseases at the single-cell level

Photocatalytic Fuel Cell-Assisted Molecularly Imprinted Self-Powered Sensor: A Flexible and Sensitive Tool for Detecting Aflatoxin B1

The self-powered electrochemical sensor has gained big achievements in energy and devices, but it is challenging in analytical application owing to its low energy conversion efficiency and limited selectivity caused by the plentiful interference in actual samples. Herein, a new self-powered biosensor was constructed by the integration of a photocatalytic fuel cell (PFC) with a molecular imprinting polymer (MIP) to achieve sensitive and specific detection of aflatoxin B1 (AFB1). Compared with other fuel cells, the PFC owns the advantages of low cost, high energy, good stability, and friendly environment by using light as the excitation source. MoS2–Ti3C2Tx MXene (MoS2–MX) served as the photoanode material for the first time by forming a heterojunction structure, which can enhance the photocurrent by about 3-fold and greatly improve the photoelectric conversion efficiency. Aiming at the poor selectivity of the self-powered sensor, the MIP was introduced to achieve the specific capture and separation of targets without sample pretreatment. Using the MIP and PFC as recognition and signal conversion elements, respectively, the proposed self-powered biosensor showed a wide dynamic range of 0.01–1000 ng/mL with a detection limit of 0.73 pg/mL, which opened opportunities to design more novel self-powered biosensors and promoted its application in food safety and environmental monitoring