Scanning Electrochemical Probe Lithography for Ultra-Precision Machining of Micro-Optical Elements with Freeform Curved Surface.

Two challenges should be overcome for the ultra-precision machining of micro-optical element with freeform curved surface: one is the intricate geometry, the other is the hard-to-machining optical materials due to their hardness, brittleness or flexibility. Here scanning electrochemical probe lithography (SECPL) is developed, not only to meet the machining need of intricate geometry by 3D direct writing, but also to overcome the above mentioned mechanical properties by an electrochemical material removal mode. Through the electrochemical probe a localized anodic voltage is applied to drive the localized corrosion of GaAs. The material removal rate is obtained as a function of applied voltage, motion rate, scan segment, etc. Based on the material removal function, an arbitrary geometry can be converted to a spatially distributed voltage. Thus, a series of micro-optical element are fabricated with a machining accuracy in the scale of 100 s of nanometers. Notably, the spiral phase plate shows an excellent performance to transfer parallel light to vortex beam. SECPL demonstrates its excellent controllability and accuracy for the ultra-precision machining of micro-optical devices with freeform curved surface, providing an alternative chemical approach besides the physical and mechanical techniques.

Design of sonochemical assisted synthesis of Zr-MOF/g-C3N4-modified electrode for ultrasensitive detection of antipsychotic drug chlorpromazine from biological samples.

The rapid fabrication is described of binary electrocatalyst based on a highly porous metal-organic framework with zirconium metal core (Zr-MOF) decorated over the graphitic carbon nitride (g-C3N4) nanosheets via facile ultrasonication method. It is used for the robust determination of antipsychotic drug chlorpromazine (CLP) from environmental samples. The electrochemical behaviour of 2D Zr-MOF@g-C3N4 was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) studies. The crystalline and porous nature of the composite was characterized by XRD and SEM analysis. The functional groups and surface characteristics were investigated by FT-IR, Raman and XPS. The major electrochemical properties of the Zr-MOF@g-C3N4 composite towards CLP detection were analyzed by CV, chronocoulometric (CC), chronoamperometric (CA) and differential pulse voltammetry (DPV) techniques. The composite exhibits a low detection limit (LOD) of 2.45 nM with a linear range of 0.02 to 2.99 µM and attractive sensitivity for CLP. The sensor system shows higher selectivity towards the possible interferences of CLP drug and exhibits better repeatability and stability. Finally, the fabricated sensor system shows a high recovery range varying from 96.2 to 98.9% towards the real samples. The proposed electrochemical probe might be a promising alternative to the prevailing diagnostic tools for the detection of CLP.

Recent Advances in Electrochemical Sensors for Formaldehyde.

Formaldehyde, a ubiquitous indoor air pollutant, plays a significant role in various biological processes, posing both environmental and health challenges. This comprehensive review delves into the latest advancements in electrochemical methods for detecting formaldehyde, a compound of growing concern due to its widespread use and potential health hazards. This review underscores the inherent advantages of electrochemical techniques, such as high sensitivity, selectivity, and capability for real-time analysis, making them highly effective for formaldehyde monitoring. We explore the fundamental principles, mechanisms, and diverse methodologies employed in electrochemical formaldehyde detection, highlighting the role of innovative sensing materials and electrodes. Special attention is given to recent developments in nanotechnology and sensor design, which significantly enhance the sensitivity and selectivity of these detection systems. Moreover, this review identifies current challenges and discusses future research directions. Our aim is to encourage ongoing research and innovation in this field, ultimately leading to the development of advanced, practical solutions for formaldehyde detection in various environmental and biological contexts.

An electrochemical sandwich immunosensor for cardiac troponin I by using nitrogen/sulfur co-doped graphene oxide modified with Au@Ag nanocubes as amplifiers.

A voltammetric sandwich immunoassay is described for the biomarker cardiac troponin I (cTnI). The gold nanocube-functionalized graphene oxide (AuNC/GO) is employed as a substrate to accelerate the electron transfer and to immobilize more primary antibodies. It also employs composite materials prepared from bimetallic gold/silver core-shell nanocubes and nitrogen and sulfur co-doped reduced graphene oxide as the signal amplifier. The introduction of N and S into GO enlarges the active surface and accelerates the electron transfer rate. Such unique characteristics render the material an effective support substrate to load more Au@AgNC and to immobilize an increasing number of second antibodies via Ag-N bonds. After specific binding with cTnI, the immunosensor was incubated in a labeled cTnI secondary antibody solution. The amperometric signal change is then measured at 0.34 V (vs. SCE) using o-phenylenediamine and hydrogen peroxide as an electrochemical probe. Response is linear in the concentration range from 100 fg∙mL-1 to 250 ng∙mL-1, and the detection limit is 33 fg∙mL-1. Graphical abstract Schematic presentation of cardiac troponin I (cTnI) electrochemical immunosensor based on gold nanocube-functionalized graphene oxide (AuNC/GO) as substrate material, bimetallic gold/silver core-shell nanocubes and nitrogen and sulfur co-doped reduced graphene oxide (Au@AgNC/N, S-rGO) as signal amplifier, and hydrogen peroxide (H2O2) and o-phenylenediamine (o-PD) as redox probe.

Scanning droplet cell for chemoselective patterning through local electroactivation of protected quinone monolayers.

A reagentless strategy for template-free patterning of uniformly inert surfaces is suggested. A layer of p-hydroquinone (HQ) protected by the tert-butyldimethylsilyl (TBDMS) group is electrografted onto glassy carbon electrodes. Chemoselective activation is performed through electrochemically controlled cleavage of the TBDMS group, which yields the redox-active surface-confined quinone moieties. The latter are shown to undergo electrochemically induced Michael addition, which serves for subsequent functionalization of the electrode surface. Patterning of the TBDMS-quinone-modified surface is accomplished by using selective localized cleavage of the protecting group. State-of-the-art direct-mode scanning electrochemical microscopy (SECM) patterning fails to yield the anticipated interfacial reaction; however, the electrochemical scanning droplet cell (SDC) is capable of conducting the localized chemoselective reaction. In a small area, dictated by the dimensions of the droplet, electrochemically induced cleavage of the protecting group can be performed locally to give rise to arrays of active quinone spots. Upon deprotection, the redox signals, attributed to the hydroquinone/benzoquinone couple, provide the first direct evidence for chemoselective electrochemical patterning of sensitive functionalities. Subsequent SECM studies of the resulting modified areas demonstrate spatial control of the proposed patterning technique.

Bi2MoO6/MWCNTs-COOH/GCE electrochemical probe for ultrasensitively and selectively detecting antibiotic norfloxacin.

Antibiotics have emerged as a class of contaminants of concern globally, raising widespread worry and unease, primarily because of their inappropriately use and endless migration in food chains. Electrochemical ultrasensitive and selective determination of norfloxacin (NOR) using bismuth-based bimetallic salt bismuth molybdate (Bi2MoO6) and carboxylated multi-walled carbon nanotube (MWCNTs-COOH) hybrid electrode as sensing platforms is presented hereby. The electrocatalytic ability of the electrodes was verified to be enhanced by the synergy effect of both Bi2MoO6 and MWCNTs-COOH using cyclic voltammetry and electrochemical impedance spectroscopy. Linear scan voltammetry was applied to detect NOR. The oxidation peak current was linearly correlated with NOR concentration of 0.03-10 µM and the low limit detection of the optimized method was 6.7 nM (S/N = 3). In addition, it was verified that Bi2MoO6/MWCNTs-COOH/GCE probe had good stability, reproducibility, repeatability and selectivity. The spiked recovery method for NOR in milk and lake water samples showed recoveries of 94.8 - 96.9% and 90.2 - 98.3%, respectively, which can be used to determine NOR in real samples with high sensitivity. The preparation of Bi2MoO6/MWCNTs-COOH/GCE provides a new prototype for probing NOR detection at nanomolar concentration and safeguarding antibiotic contamination in environmental and food chains.

N-methyl mesoporphyrin IX (NMM) as electrochemical probe for detection of guanine quadruplexes.

G-quadruplexes (G4) are stable alternative secondary structures of nucleic acids. With increasing understanding of their roles in biological processes and their application in bio- and nanotechnology, the exploration of novel methods for the analysis of these structures is becoming important. In this work, N-methyl mesoporphyrin IX (NMM) was used as a voltammetric probe for an easy electrochemical detection of G4s. Cyclic voltammetry on a hanging mercury drop electrode (HMDE) was used to detect NMM with a limit of detection (LOD) of 40 nM. Characteristic reduction signal of NMM was found to be substantially higher in the presence of G4 oligodeoxynucleotides (ODNs) than in the presence of single- or double-stranded ODNs and even ODNs susceptible to form G4s but in their unfolded, single-stranded forms. Gradual transition from unstructured single strand to G4, induced by increasing concentrations of the G4 stabilizing K+ ions, was detected by an electrochemical method for the first time. All obtained results were supported by circular dichroism spectroscopy. This work expands on the concept of electrochemical probes utilization in DNA secondary structure recognition and offers a proof of principle that can be potentially employed in the development of novel electroanalytical methods for nucleic acid structure studies.

Controllable preparation of silver-doped hollow carbon spheres and its application as electrochemical probes for determination of glycated hemoglobin.

Silver-doped hollow carbon spheres (Ag@HCS) were firstly introduced as electrochemical probes for glycated hemoglobin (HbA1c) sensing at a molecularly imprinted polymer (MIP)-based carbon cloth (CC) electrode. Herein, Ag@HCS was prepared using one-pot polymerization of resorcinol and formaldehyde with AgNO3 on the SiO2 template, subsequent carbonization, and template removal. Furthermore, poly-aminophenylboronic acid (PABA) as the MIP film was used as a sensing platform for recognition of HbA1c, which captured the Ag@HCS probe by binding of HbA1c with aptamer modified on the probe surface. Due to regular geometry, large specific surface area, superior electrical conductivity, and highly-dispersed Ag, the prepared Ag@HCS probe provided an amplified electrochemical signal based on the Ag oxidation. By use of the sandwich-type electrochemical sensor, the ultrahigh sensitivity of 4.365 µA (µg mL-1)-1 cm-2 and a wide detection range of 0.8-78.4 µg mL-1 for HbA1c detection with a low detection limit of 0.35 µg mL-1 were obtained. Excellent selectivity was obtained due to the specific binding between HbA1c and PABA-based MIP film. The fabricated electrochemical sensing platform was also implemented successfully for the determination of HbA1c concentrations in the serum of healthy individuals.

Bifunctional cyclomatrix polyphosphazene-based hybrid with abundant decorating groups: Synthesis and application as efficient electrochemical Pb(II) probe and methylene blue absorbent.

HYPOTHESIS: The construction of novel functional cyclomatrix polyphosphazenes (CPPs) hybrid, which with diverse decorating groups, is a challenging task due to the structural limitation of available reaction substrates (phenols and amines). EXPERIMENTS: Herein, a phenolic hydroxyl (OH) modified ployamide derivative (P2) was successfully prepared via novel benzoxazine-isocyanide chemistry (BIC). A kind of CPP hybrid (P3), which with abundant functional groups (amide, tertiary amine, benzoxazine and phenolic hydroxyl) was prepared subsequently by the condensation between P2 and hexachlorocyclotriphosphazene (HCCP). Chemical structure, elemental composition, morphology, porous properties and crystallinity of P3 were systematically analyzed here. The electrochemical detection of lead ion (Pb2+) was realized by using P3-modified glassy carbon electrode (GCE/Nafion/P3) as the working electrode. Besides this, given the unique chemical structure and morphology of P3, the selective adsorption of methylene blue (MB) by P3 was also studied here. FINDINGS: Experimental results indicated that that P3 can act as bifunctional hybrid material to solve environmental issues.

Latent Redox Reporter of 4-Methoxyphenol as Electrochemical Signal Proxy for Real-Time Profiling of Endogenous H2O2 in Living Cells.

Hydrogen peroxide (H2O2) plays a persuasive role in the human cell physiology. Developing an efficient assay platform and a highly sensitive tracking and quantification of H2O2 in a physiological system is crucial to understand the neoplastic changes and/or redox homeostasis of cells. In this study, a novel turn-on latent electrochemical redox probe coupled with electrocatalytic signal amplification strategy is proposed. A custom-made readily available turn-on latent electrochemical probe 4-methoxyphenylboronic acid pinacol ester (4-MPBP) have been designed for the selective detection of endogenous H2O2 in live cells. The electrochemical probe composed of a latent electrochemical reporter (4-methoxy phenol, 4-MP) bearing a recognition unit (boronic acid pinacol ester) for H2O2 sensing. The selective analyte-triggered chemical transformation releases free electrochemical reporter 4-MP. The amount of H2O2 was evaluated electrochemically at glassy carbon electrode (GCE) with a broad detection range of 0.5 µM-1 mM. An amplified signal response of released 4-MP to build a highly sensitive assay tool has been achieved via replacing the GCE transducer electrode with polydopamine@carbonnanotube-molebtinumdisulfie hybrid modified GCE as it delivered an exceptional dynamic detection range of 0.01-100 µM. The innovative blend of electrochemical molecular probe strategy, with electrocatalytic signal amplification technique has delivered outstanding assay performance at trace level sensing of H2O2. Next, we set up a platform for real-time in vivo monitoring of the endogenously produced H2O2 in Caco-2 and MCF-7 cells through spermine-polyamine analogue and phorbol 12-myristate 13-acetate induction in SSAT/PAO gene and protein kinase C, respectively. As expected, the 4-MPBP latent probe coupled with electrocatalytic signal amplification strategy delivered outstanding performance for in situ H2O2 release and tracking over time.