Fluorescence determination of the total amount of tetracyclines by a flavonol-based supramolecular sensor

Albumin host for supramolecular fluorescence recognition

Synthetic molecular sensors are crucial for real-time monitoring in biological systems and biotechnological applications, where detecting targets amidst potential interferents is essential. This task is particularly challenging in competitive environments that lacking chemically reactive functional groups, common in agricultural, biological, and environmental contexts. Consequently, scientific efforts have focused on developing sensitive and rapid analytical techniques, with fluorescent sensors emerging as prominent tools. Among these, the albumin-based supramolecular fluorescent indicator displacement assay (AS-FIDA) represents a significant advancement. Our research group has extensively contributed to this field, demonstrating the practical utility of various AS-FIDAs. We pioneered the use of albumin (ALB) as a host molecule in these synthetic chemical sensors, marking a notable advancement. AS-FIDA employs ALB as a versatile host molecule with multiple flexible and asymmetrical binding pockets capable of forming complexes with guest dyes, resulting in ALB@dye ensembles tailored for specific analyte recognition. Recent advancements in AS-FIDA have significantly expanded its applications. This review explores recent advances in ALB-based supramolecular sensors and sensor arrays for detecting biologically and environmentally significant molecules, such as pesticides, hormones, biomarkers, reactive species, mycotoxins, drugs, and carcinogens. The versatility of AS-FIDA positions it as a valuable tool in diverse settings, from laboratory research to practical applications in portable devices, smartphone-assisted on-site monitoring, imaging of living cells, and real sample analysis.

Rational design of a dual-mode fluorescent probe for portable detection of pyriproxyfen in the environment and food

The development of a fluorescent probe for pyriproxyfen (PPF) is crucial due to its potential threat to human health. However, the chemical inertness and low solubility of PPF present significant challenges for the detection of PPF in aqueous solutions using fluorescent probes. Herein, we have originally proposed a complex based on 2-(4-(dimethylamino)phenyl)-3-hydroxy-6,7-dimethoxy-4 H-chromen-4-one (HOF) and serum albumin (SA) as a dual-mode fluorescent probe, HOF@SA. This probe utilizes an indicator displacement assay (IDA) to release the dye HOF from the probe at low PPF concentrations (< 10 µM) and embeds the free dye HOF into the micelle of PPF at high concentrations (> 10 µM). This results in dual-mode fluorescent response characteristics for PPF: a turn-off response at low concentrations and a ratiometric response at high concentrations. An investigation of sensing behavior of HOF@SA for PPF detection exhibits rapid response (< 60 s), high sensitivity (LOD ∼4.7 ppb), high selectivity, and excellent visual detection capability (from cyan to yellow). Moreover, with the aid of a portable device, this method enables to analyze PPF in environmental and food samples. These results promote the advancement of a fluorescent probe approach for PPF analysis in environment and food.

Natural flavonols as probes for direct determination of borax: From conventional fluorescence analysis to paper-based smartphone sensing

Borax is strictly regulated in the food processing and pharmaceutical industry due to its physiological toxicity, and the development of a direct analytical method is essential for effectively monitoring the borax abuse. In this work, the fluorescence properties of flavonoids, including flavones, isoflavones and flavonols, were systematically investigated from aqueous to borax solutions, and it was found that the weak intrinsic fluorescence of flavonols could be pervasively sensitized by borax. A natural flavonol, morin, was subsequently chosen as a representative probe to develop a turn-on fluorescence sensing method for borax analysis, which achieved a linear response spanning four orders of magnitude with a detection limit of 1.07 μM (0.22 μg mL-1 in terms of Na2B4O7 content). Furthermore, a smartphone-assisted paper-based test device was designed and constructed by 3D printing technology. Using morin-impregnated test strips as the carrier, the borax could be visually detected by the RGB signals of the captured images, with a detection limit of 0.13 mM (27.05 μg mL-1 for Na2B4O7). Combining ion exchange treatment for food samples and sodium periodate oxidation for drug samples, the developed methods were successfully applied for the direct analysis of borax in various products with the recoveries of 86.9-106.3% for traditional fluorescence analysis and 82.7-108.8% for smartphone-assisted fluorescence sensing. The fluorescence property of the morin-borax system was studied using time-dependent density functional theory, and the sensing mechanism was discussed in conjunction with experimental research.

An antifouling electrochemical aptasensor based on a polydopamine-polyzwitterion copolymer for tetracycline analysis

Matrix interference resulting from the nonspecific adsorption of non-target components, particularly proteins (fouling), onto sensor surfaces poses a persistent challenge in electrochemical detection of food hazards. The development of antifouling sensor surfaces presents a viable approach to mitigate nonspecific adsorption. In this study, a novel antifouling electrochemical aptasensor, utilizing a zwitterionic polymer, was developed for the sensitive, accurate, and selective detection of tetracycline (TC) in milk. This sensor employs a poly (dopamine)-poly (sulfobetaine methacrylate) (PDA-PSBMA) antifouling copolymer, which is synthesized through an in-situ initiated copolymerization of dopamine on the sensor's surface. Subsequently, the thiol-containing aptamers were immobilized onto the PDA-PSBMA coating through a Michael addition reaction with the poly(dopamine). The resulting antifouling electrochemical aptasensor exhibited robust antifouling performance in various single protein solutions and diluted milk samples, coupled with sensitive and selective recognition of TC. The sensor demonstrated a broad linear response range of 0.1-1000.0 ng mL-1 and a low limit of detection (LOD) of 68.0 pg mL-1. The antifouling electrochemical aptasensor proved effective in assaying TC in diluted milk, with recoveries ranging from 100.0 % to 104.4 %, eliminating the need for additional pretreatments due to its exceptional resistance to nonspecific adhesion.

TPN-COF@Fe-MIL-100 composite used as an electrochemical aptasensor for detection of trace tetracycline residues

In this work, a metal-organic framework@covalent organic framework composite (TPN-COF@Fe-MIL-100) was prepared and used as a sensing material to construct an aptasensor for trace detection of tetracycline (TET). The TPN-COF@Fe-MIL-100 integrates a large surface area, porous structure, excellent electrochemical activity, rich chemical functionality, and strong bioaffinity for aptamers, providing abundant active sites to effectively anchor aptamer strands. As a result, the TPN-COF@Fe-MIL-100-based aptasensor shows high sensitivity for detecting TET via specific recognition between aptamer and TET to form G-quadruplex. An ultralow detection limit of 1.227 fg mL-1 is deduced from the electrochemical impedance spectroscopy within a wide linear range of 0.01-10000 pg mL-1 for TET. The TPN-COF@Fe-MIL-100-based aptasensor also exhibits good selectivity, reproducibility, stability, regenerability, and applicability for a real milk sample. Therefore, the TPN-COF@Fe-MIL-100-based aptasensor will be promising for detecting trace harmful antibiotics residues for food safety.