Design of Cyclic Peptide Based Glucose Receptors and Their Application in Glucose Sensing

Glucose assay is of great scientific significance in clinical diagnostics and bioprocess monitoring, and to design a new glucose receptor is necessary for the development of more sensitive, selective, and robust glucose detection techniques. Herein, a series of cyclic peptide (CP) glucose receptors were designed to mimic the binding sites of glucose binding protein (GBP), and CPs’ sequence contained amino acid sites Asp, Asn, His, Asp, and Arg, which constituted the first layer interactions of GBP. The properties of these CPs used as a glucose receptor or substitute for the GBP were studied by using a quartz crystal microbalance (QCM) technique. It was found that CPs can form a self-assembled monolayer at the Au quartz electrode surface, and the monolayer’s properties were characterized by using cyclic voltammetry, electrochemical impedance spectroscopy, and atomic force microscopy. The CPs’ binding affinity to saccharide (i.e., galactose, fructose, lactose, sucrose, and maltose) was investigated, and the CPs’ sensitivity and selectivity toward glucose were found to be dependent upon the configuration,i.e., the amino acids sequence of the CPs. The cyclic unit with a cyclo­[-C<b>NDNH</b>C<b>RDND</b>C-] sequence gave the highest selectivity and sensitivity for glucose sensing. This work suggests that a synthetic peptide bearing a particular functional sequence could be applied for developing a new generation of glucose receptors and would find huge application in biological, life science, and clinical diagnostics fields

Development of an Enzyme-Linked Immunosorbent Assay for the Detection of Tyramine as an Index of Freshness in Meat and Seafood

A competitive indirect enzyme-linked immunosorbent assay (ciELISA) using a polyclonal antibody was developed to detect tyramine in meat and seafood. This ciELISA had a 50% inhibition concentration (IC₅₀) of 0.20 mg/L and a limit of detection (LOD) of 0.02 mg/L and showed no cross-reactivity with tyrosine or other biogenic amines. The average recoveries of tyramine from spiked samples for this ciELISA ranged from 85.6 to 102.6%, and the results exhibited good correlation with high-performance liquid chromatography (HPLC) results. The LOD of this assay for tyramine in meat and seafood samples was 1.20 mg/kg. The ciELISA was successfully applied to detect tyramine in positive fish samples, and the results were validated by HPLC to be reliable. The developed ciELISA allows for the rapid, specific, and accurate detection of tyramine in meat and seafood samples, and it could be a potentially useful tool for the evaluation of the freshness of protein-rich foods

Highly Bright Self-Assembled Copper Nanoclusters: A Novel Photoluminescent Probe for Sensitive Detection of Histamine

In this work, highly photoluminescent (PL) self-assembled copper nanoclusters (Cu NCs) capable of rapid, sensitive, and selective detection of histamine were developed. Cu NCs were synthesized in facile conditions by using 2,3,5,6-tetrafluorothiophenol (TFTP) as both the reducing agent and the protecting ligand, which exhibited intense saffron yellow (590 nm) PL via self-assembled induced emission (SAIE), and the absolute quantum yield (QY) of assembly was as high as 43.0%. The size, electronic states, and morphologies of the assembled nanoribbons were characterized, and the geometric structure and spectral properties of the Cu NCs were investigated by theoretical study. Furthermore, the mechanism of the excellent sensing performance of Cu NCs toward histamine was demonstrated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and energy dispersive X-ray analysis (EDX). With this sensing system, the amount of histamine in fish, shrimp, and red wine were analyzed, and experiment results verified the application of the sensor. Importantly, the luminescent test strips based on Cu NCs were fabricated for colorimetric detection of histamine in foods. This proposed technique may provide an alternative to traditional methods for histamine detection