Background Microbial contamination is an increasing concern in the food industry. In order to understand the effect of microorganisms, the study of their characteristics and behavior in various platforms is of prime importance. Over the years, time-consuming and labor-intensive, culture-based enumeration techniques have become obsolete for real-time applications, and increasing concerns on foodborne outbreaks necessitate rapid, on-site and sensitive methods for the detection of microorganisms in food matrices. Scope and approach In the current review, a brief discussion about biomarkers in microorganisms and bio-recognition ligands commonly used for detection assay are presented. The molecular interaction between biomarkers and ligands is critically evaluated and recent developments in bio-recognition based detection techniques for analyzing microorganism activity in complex food matrices are reviewed. Key findings and conclusions The microbial activity in food can be detected by analyzing the specific biomarkers of microorganisms such as nucleic acids, proteins, antigens, and metabolic products. Recent bio-recognition ligands in detection techniques such as biosensors, lateral flow assay, and microfluidic devices can improve the selectivity in detecting cells from complex food matrices. The emerging bio-recognition based methods bridge the gap between culture-dependent enumeration and molecular methods, and they could be employed in the industry to ensure food safety. However, the development of a validation protocol for all the emerging methods is necessary to assess their efficiency in real samples.

Recent development in rapid detection techniques for microorganism activities in food matrices using bio-recognition: A review

A smartphone-integrated ratiometric fluorescence sensing platform for visual and quantitative point-of-care testing of tetracycline

Fluorescence quantum dots (QDs) are promising functional nanomaterials in chemical biology and environmental applications, where an analyte-induced responsive system is beneficial for detecting numerous life-related molecules and pollutants. Here, fluorescent Ti3C2 MXene quantum dots (MQDs) with the size of 1.75 nm were synthesized by a simple method of hydrofluoric acid etching and dimethyl sulfoxide exfoliation to form nanosheets followed by a one-step ultrasound method. The as-synthesized MQDs showed excitation-dependent behaviour along with a fluorescence quantum yield value of 7.7%. In addition, the fluorescence of the MQDs can be significantly suppressed by Fe3+. The mechanism for the fluorescence quenching of the MQDs was systematically investigated, which was attributed to the oxidation-reduction reaction between the MQDs and Fe3+ and the inner filter effect (IFE), different from the reported Forster resonant energy transfer (FRET) mechanism for MXene nanosheets. Based on this trait, a fluorescence method for Fe3+ detection based on MQDs was demonstrated with high sensitivity and selectivity, and the limit of detection was 310 nM. The proposed method was successfully used for the sensitive detection of Fe3+ in serum and sea water. This work will not only help to understand the selectivity mechanisms of MQDs as fluorescent probes for metal ions, but also provide a smart sensing platform in biological and environmental detection.

Selective detection of Fe3+ ions based on fluorescence MXene quantum dots via a mechanism integrating electron transfer and inner filter effect

On account of the excessive residues and serious detriments, it is imminent to develop an efficient method to determine tetracyclines (TCs) for protecting human health. In this work, a novel ratiom...

Innovative Dual-Emitting Ratiometric Fluorescence Sensor for Tetracyclines Detection Based on Boron Nitride Quantum Dots and Europium Ions

Development of selective and sensitive methods for on-site assay of tetracycline (TC) is of great significance for public health and food safety. Herein, a valid ratiometric fluorescence strategy using g-C3N4 nanosheets coupled with Eu3+ is designed for the assay of TC. In this strategy, both Eu3+ and g-C3N4 nanosheets serve as the recognition units of TC. The blue fluorescence of g-C3N4 nanosheets can be quenched by TC via the inner filter effect (IFE); meanwhile, the red fluorescence of Eu3+ can be enhanced by TC through the antenna effect (AE). The synergistic effect of AE and IFE caused by TC makes the developed ratiometric fluorescent sensor display a wide linear range for TC from 0.25 to 80 μM with a detection limit of 6.5 nM and a significant fluorescence color evolution from blue to red. Given its simplicity, free-label, excellent selectivity, high sensitivity, and recognizable color change, point-of-care testing systems, including smartphones and test paper-based assays, are developed for the visual sensing of TC. The integration of smartphones and test paper on a ratiometric fluorescent sensor greatly reduces the detection cost and time, providing a promising method for the qualitative discernment and semi-quantitative assay of TC on-site. Moreover, the potential application of the approach is also verified by detecting TC in milk.

Smartphones and Test Paper-Assisted Ratiometric Fluorescent Sensors for Semi-Quantitative and Visual Assay of Tetracycline Based on the Target-Induced Synergistic Effect of Antenna Effect and Inner Filter Effect

A sensitive and selective approach for detection of tetracyclines using fluorescent molybdenum disulfide nanoplates.

The authors describe a simple and economical fluorescence method for the determination of nitrite by utilizing the fact that nitrite possesses strong oxidation in acidic solution and is capable to transform iron(II) into iron(III) ions. The latter quenches the fluorescence of carbon quantum dots (CQDs) based on the fluorescence static and dynamic quenching effect. The optimum reaction conditions and other analytical parameters are investigated to enhance the sensitivity of the method. At the excitation wavelength of 360 nm, this probe has a linear response in the 10 to 400 μM nitrite concentration range, with a correlation coefficient of R2 = 0.9958 (n = 3) and a detection limit of 0.48 μM. This method was successfully applied to the determination of nitrite in three different sausage samples and gave recoveries in the range between 101.8 to 103.0%, demonstrating the accuracy, reliability and potential application of this assay for monitoring nitrite. Graphical Abstract The carbon quantum dot/iron(II) ions system was used for the fluorometric detection of nitrite in food and environmental water. This probe exploits the oxidizing property of nitrite in acidic solution. Iron(II) is oxidized to iron(III) which exerts a strong fluorescence quenching effect.

Carbon quantum dot-based fluorometric nitrite assay by exploiting the oxidation of iron(II) to iron(III).

Gold nanoparticles (AuNPs)-based lateral flow strip (LFS) enables a quick screening of foodborne bacteria in point-of-care (POC) diagnostics but suffers from the cumbersome labeling of antibodies and poor sensitive performance. Here, we innovated a label-free immunoassay to detect pathogenic bacteria by introducing diversely positive charges functionalized AuNPs ((+) AuNPs). The (+) AuNPs can be loaded on negatively charged bacteria via electrostatic interaction, leading to a color labeling to target bacteria. Afterward, the (+) AuNPs-bacteria complex can be specifically captured by monoclonal antibody (McAb) immobilized on test (T)-line. Under optimum conditions, the proposed LFS exhibited a lowest detectable concentration of 103 CFU/mL for Salmonella enteritidis (S. enteritidis) and could be well applied in drinking water, lettuce and pork samples. Moreover, this novel (+) AuNPs-LFS possessed a universal applicability, which could also be used for detecting Escherichia coli O157 (E. coli O157) with a superior sensitivity (104 CFU/mL) and specificity.

Diversely positive-charged gold nanoparticles based biosensor: A label-free and sensitive tool for foodborne pathogen detection

Visual and fluorescent detection of mercury ions using a dual-emission ratiometric fluorescence nanomixture of carbon dots cooperating with gold nanoclusters.

Jinghan Liu

Papers

A sensitive and selective approach for detection of tetracyclines using fluorescent molybdenum disulfide nanoplates.

Carbon quantum dot-based fluorometric nitrite assay by exploiting the oxidation of iron(II) to iron(III).

Diversely positive-charged gold nanoparticles based biosensor: A label-free and sensitive tool for foodborne pathogen detection

Visual and fluorescent detection of mercury ions using a dual-emission ratiometric fluorescence nanomixture of carbon dots cooperating with gold nanoclusters.