Faradaic Counter for Liposomes Loaded with Potassium, Sodium Ions, or Protonated Dopamine

Impact electrochemistry for biosensing: advances and future directions

Impact electrochemistry allows for the investigation of the properties of single entities, ranging from nanoparticles (NPs) to soft bio-particles. It has introduced a novel dimension in the field of biological analysis, enhancing researchers' ability to comprehend biological heterogeneity and offering a new avenue for developing novel diagnostic devices for quantifying biological analytes. This review aims to summarize the recent advancements in impact electrochemistry-based biosensing over the past two to three years and provide insights into the future directions of this field.

Elucidating the Shape of Current Transients in Electrochemical Resistive-Pulse Sensing of Single Liposomes

Electrochemical resistive-pulse (ERP) sensing with conductive carbon nanopipettes (CNPs) has recently been developed and employed for the detection of single liposomes and biological vesicles, and for the analysis of redox molecules contained in such vesicles. However, the origins of different shapes of current transients produced by the translocation of single vesicles through the CNP remain poorly understood. Herein, we report extensive finite-element simulations of both portions of an ERP transient, the current blockage by a vesicle approaching and passing through the pipet orifice and the faradaic current spike due to oxidation/reduction of redox species released from a vesicle on the carbon surface, for different values of parameters defining the geometry and dynamics of the vesicle/CNP system. The effects of the pipet geometry, surface charge, transport, vesicle trajectory, and collision location on the shape of current transients are investigated. The possibility of quantitative analysis of experimental ERP transients produced by translocations of liposomes and extracellular vesicles by fitting them to simulated curves is demonstrated. The developed theory can enable a more reliable interpretation of complicated ERP signals and characterization of the size and contents of single biological and artificial vesicles.

Magnetic Rolling Circle Amplification-Assisted Single-Particle Collision Immunosensor for Ultrasensitive Detection of Cardiac Troponin I

Owing to its simplicity, high throughput, and ultrasensitivity, single-particle collision electrochemistry (SPCE) has attracted great attention in biosensing, especially labeled SPCE. However, the low signal conversion efficiency and much interference from complex samples limit its wide application. Here, a new and robust SPCE immunosensor was proposed for ultrasensitive cardiac troponin I (cTnI) detection by combining target-driven rolling circle amplification (RCA) with magnetic beads (MBs). Antibody-modified MBs have good stability, dispersity, and magnetic response capacity in complex samples, enabling efficient capture and separation of cTnI with high specificity and anti-interference ability. The presence of cTnI could specifically drive the formation of magnetic immunocomplexes followed by triggering RCA and enzyme digestion reaction. By using Pt nanoparticles (Pt NPs)-modified ssDNA as signal probes, one cTnI molecule could induce the release of 4.5 × 10⁴ Pt NPs for collision experiments, greatly enhancing signal conversion efficiency and detection sensitivity. Based on the integration of MBs with RCA, the SPCE immunosensor realized 0.57 fg/mL cTnI detection with a wide linear range of 1 fg/mL to 50 ng/mL. Furthermore, cTnI detection in serum samples of myocardial infarction patients was successfully performed, demonstrating great application prospect of the SPCE immunosensor in clinical diagnosis.

Defined Ion-Transfer Voltammetry of a Single Microdroplet at a Polarized Liquid/Liquid Interface

A strategy for the fast analysis of ion transfer/facilitated ion transfer toward a tiny (femtoliter) water-in-oil droplet has been established. This scenario is embodied by the fusion of a w/o microdroplet at the micro liquid/liquid (L/L) interface, with the use of Fourier transform fast-scan cyclic voltammetry (FT-FSCV) to express the apparent half-wave potentials of anions or cations encapsulated inside the w/o microdroplet. First, the half-wave potential is in strict accordance with the transfer Gibbs free energy of either cations or anions. Second, the half-wave potential has been found to be positively proportional to the logarithmic concentration of ions, shedding thermodynamic insight into ion transfer. Third, as an instance of multivalent biopolymers, the transfer of protamine inside the single w/o microdroplet has been investigated. Obvious discrepancies in the behaviors of the fusion impacts at different pH, as well as in the absence and presence of the cationic surfactant DNNS^-, are revealed. The internal mechanism of protamine transfer has been thoroughly investigated. This work proposes a strategy to sensitively and quickly determine the transfer Gibbs energy and the concentration of ions encapsulated in a single microdroplet, and it provides the possibility of analyzing the interfacial transfer properties of trace biomacromolecules inside an aqueous micro- or nanoscale droplet.