Evaluation of covalent coupling strategies for immobilizing ligands on silica colloidal crystal films by optical interferometry

Immobilizing ligands is a crucial part of preparing optical sensors and directly connected to the sensitivity, stability, and other characteristics of sensors. In this work, an ordered porous layer interferometry (OPLI) system that can monitor the covalent coupling process of ligands in real time was developed. Films of silica colloidal crystal (SCC), as optical interference substrates, were surface modified by three different reagents: chloroacetic acid, glutaric anhydride, and carboxymethyl dextran. Staphylococcus aureus protein A (SPA), the ligand, was immobilized on SCC films. The covalent coupling process of SPA and SCC films can be dynamically monitored by the OPLI system. In addition, the three different strategies were evaluated by comparing the efficiency of the sensors prepared by different methods for binding Immunoglobulin G (IgG). The glutaric anhydride-modified sensor offers apparent advantages in terms of bound IgG quantity and affinity. This system provides a simple and intuitive way to determine the efficiency of different covalent coupling strategies. Furthermore, the sensor covalently coupled with SPA also excels in the determination of IgG content in complex systems such as milk. At the same time, the covalent coupling gives the sensor the ability to be stored stably over time.

Electrochemical sensor based on novel two-dimensional nanohybrids: MoS2nanosheets conjugated with organic copper nanowires for simultaneous detection of hydrogen peroxide and ascorbic acid

MoS₂nanosheets were conjugated with organic copper nanowires for fabrication of electrochemical hydrogen peroxide and ascorbic acid sensors.

Recent Advances in the Fabrication and Application of Screen-Printed Electrochemical (Bio)Sensors Based on Carbon Materials for Biomedical, Agri-Food and Environmental Analyses

This review describes recent advances in the fabrication of electrochemical (bio)sensors based on screen-printing technology involving carbon materials and their application in biomedical, agri-food and environmental analyses. It will focus on the various strategies employed in the fabrication of screen-printed (bio)sensors, together with their performance characteristics; the application of these devices for the measurement of selected naturally occurring biomolecules, environmental pollutants and toxins will be discussed.

Supramolecular biosensors based on electropolymerised pyrrole–cyclodextrin modified surfaces for antibody detection

The self-assembly of an adamantane-appended polymer bearing an antigen fragment on a polypyrrole–cyclodextrin modified surface provides a highly sensitive immunosensor with low limits of detection for celiac disease related antibodies.

A miniaturized electrochemical assay for homocysteine using screen-printed electrodes with cytochrome c anchored gold nanoparticles

Electrochemical point-of-care analysis of homocysteine in a drop of the blood plasma samples.

Designing label-free electrochemical immunosensors for cytochrome c using nanocomposites functionalized screen printed electrodes

We have designed here a label-free direct electrochemical immunosensor for the detection of cytochrome c (cyt c), a heme containing metalloprotein using its specific monoclonal antibody. Two nanocomposite-based electrochemical immunosensor platforms were evaluated for the detection of cyt c; (i) self-assembled monolayer (SAM) on gold nanoparticles (GNP) in polypyrrole (PPy) grafted screen printed electrodes (SPE) and (ii) carbon nanotubes (CNT) integrated PPy/SPE. The nanotopologies of the modified electrodes were confirmed by scanning electron microscopy. Electrochemical impedance spectroscopy and cyclic voltammetry were employed to monitor the stepwise fabrication of the nanocomposite immunosensor platforms. In the present method, the label-free quantification of cyt c is based on the direct electron transfer between Fe (III)/Fe (II)-heme redox active site of cyt c selectively bound to anti-cyt c nanocomposite modified SPE. GNP/PPy and CNT/PPy nanocomposites promoted the electron transportation through the conductive pore channels. The overall analytical performance of GNP/PPy based immunosensor (detection limit 2 nM; linear range: 2 nM to 150 µM) was better than the anti-cyt c/CNT/PPy (detection limit 10 nM; linear range: 10 nM to 50 µM). Further, the measurement of cyt c release in cell lysates of cardiomyocytes using the GNP/PPy based immunosensor gave an excellent correlation with standard ELISA.

High-performance supercapacitor electrodes based on graphene hydrogels modified with 2-aminoanthraquinone moieties

2-Aminoanthraquinone (AAQ) molecules were covalently grafted onto chemically modified graphene (CMG), and the AAQ functionalized CMG sheets were self-assembled into macroporous hydrogels for supercapacitor electrodes. The electrode based on the AAQ modified self-assembled graphene hydrogel (AQSGH) showed a high specific capacitance of 258 F g(-1) at a discharge current density of 0.3 A g(-1), which is much larger than that of a pure graphene hydrogel (193 F g(-1)). Furthermore, the AQSGH electrode exhibited excellent rate capability and a long cycle life. This is mainly due to the covalently bonded AAQ moieties contributing additional redox capacitance. Furthermore, the highly conductive graphene hydrogel scaffold provided a large specific surface area for forming electric double layers and convenient routes for charge transfer and electrolyte diffusion.

Analytical methods for heavy metals in herbal medicines

INTRODUCTION

It is estimated that about 70-80% of the world's population relies on non-conventional medicine, mainly of herbal origin. However, owing to the nature and sources of herbal medicines, they are sometimes contaminated with toxic heavy metals such as lead, arsenic, mercury and cadmium, which impose serious health risks to consumers. It is critical to analyse source materials for heavy metals in order to ensure that their concentrations meet the related standards or regulations limiting their concentrations in herbal medicines. In this review, different analytical methods for analysis of heavy metals in herbal medicines are discussed.

OBJECTIVE

To provide a comprehensive review of the current state of the art in analytical methods used to detect heavy metals in herbal medicines.

METHODOLOGY

We systematically searched and reviewed the research articles regarding analytical methods for heavy metals in herbal medicine from various databases, such as Medline/PubMed, ScienceDirect, SciFinder, Google Scholar, EBSCO, Gale InfoTrac, Ingenta, Ovid, ProQuest and ISI Web of Knowledge.

RESULTS

In this review, we discuss in detail several commonly used and sensitive analytical techniques, including atomic absorption spectrometry, inductively coupled plasma optical emission spectrometry or mass spectrometry, X-ray fluorescence spectrometry, high-performance liquid chromatography, differential pulse polarography, neutron activation analysis and anodic stripping voltammetry. We also provide some application examples of these analytical techniques for heavy metals in herbal medicines.