A paper-based microfluidic sensor array combining molecular imprinting technology and carbon quantum dots for the discrimination of nitrophenol isomers

Centrifugated lateral flow assay strips based on dual-emission carbon dots modified with europium ions for ratiometric determination and on-site discrimination of tetracyclines in environment

Due to the serious detrimental impact on human health, antibiotic pollution particularly tetracyclines residues has become a serious problem. Herein, a multiple response fluorescent probe consisted of dual-emission carbon dots and Eu3+ (D-CDs@Eu3+) is designed for the determination and discrimination of tetracyclines (TCs). Specifically, the carboxyl and amidogen group of dual-emission carbon dots (D-CDs) can coordinate with Eu3+ to form the D-CDs@Eu3+. Upon adding TCs, the fluorescence intensities of D-CDs at 405 nm and 495 nm are quenched due to inner filter effect (IFE) and the localization of fluorescence resonance energy transfer (L-FRET) between the D-CDs@Eu3+ and TC. Simultaneously, the D-CDs@Eu3+ may chelate with TCs to enhance the occurrence of antenna effect, while the characteristic peaks of Eu3+ at 590 nm and 615 nm are enhanced. On these bases, the TCs detection is achieved with low detection limits from 46.7 to 72.0 nM. Additionally, through the distinct efficiencies of L-FRET, the discrimination of TCs is achieved. Moreover, a novel centrifugated lateral flow assay strips (CLFASs) device is developed by integrating the D-CDs@Eu3+, lateral flow assay strips and smartphone using RGB variations for TCs detection, achieving remarkable recoveries (98.6-103.7 %) in real samples. Therefore, this CLFASs device provides a reliable approach for the TCs detection, demonstrating potential applications.

Portable alkaloid discrimination via nanozyme-mediated colorimetric paper-based sensor array integrated with smartphone detection

A paper-based colorimetric sensor array mediated by a novel nanozyme (CuCo2O4) was developed using a screen-printing technology. The aim was to facilitate the identification of different kinds of alkaloids. Typically, three chromogenic substrates (3,3',5,5'-tetramethylbenzidine, 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid), and o-phenylenediamine) were selected as sensing elements, which can be catalyzed by a CuCo2O4 nanozyme with peroxidase-like activity to yield corresponding oxidized products, thereby inducing color changes. Owing to the varying inhibitory ability of different alkaloids on acetylcholinesterase (AChE), a decrease in choline (Ch) concentration occurs and subsequently results in the restoration of color within the units of sensor array. Color data can be transformed into hue information with a smartphone. The above color variations generated a unique "fingerprint" pattern on five alkaloids (berberine, palmatine, jatrorrhizine, eserine, and harmane), which can be successfully discriminated through linear discriminant analysis in the range 0.2 to 20 µM. Furthermore, the sensor arrays allowed successful discrimination of the above five alkaloids in Chinese herbal medicine samples and recognition of 22 blind samples. This work presents a novel nanozyme-based paper sensor array, which is a user-friendly and reliable platform for probing different alkaloids. In addition, the developed sensing strategy enables the identification of AChE-related diseases, positively contributing to the screening available of AD-associated drugs.

A remote-controlled portable workstation for highly sensitive and real-time chemiluminescent detection of cadmium

The prevention of pollution requires real-time monitoring of cadmium (Cd2+) concentration in the food, as it has a dramatic impact on poultry and can pose a threat to human health. Here, we fabricate a portable workstation integrating a microfluidic chip that facilitates real-time monitoring of Cd2+ levels in real samples by utilizing the Luminol-KMnO4 chemiluminescence (CL) system. Interestingly, Cd2+ can significantly enhance the CL signal, resulting in sensitive detection of Cd2+ in the range of 0-0.18 mg/L with the limit of detection (LOD) of 0.207 μg/L. Furthermore, a remote-controlled unit is integrated into the portable workstation to form a remote-controlled portable workstation (RCPW) performing automated point-of-care testing (POCT) of Cd2+. The as-prepared strategy allows remote control of RCPW to avoid long-distance transportation of samples to achieve real-time target monitoring. Consequently, this system furnishes RCPW for monitoring Cd2+ levels in real samples, thereby holding potential for applications in preventing food pollution.

Distinct influence of model electron shuttles on anaerobic mononitrophenols reduction in aquatic environments by Shewanella oneidensis MR-1

The environmental fate and risks of mononitrophenols (mono-NPs), the simplest nitrophenols (NPs) often found in aquatic environments, are profoundly influenced by anaerobic bioreduction and co-existing electron shuttles (ESs), but little is known about the underlying mechanisms. Here, we elucidate the pathways of anaerobic mono-NPs bioreduction by Shewanella oneidensis MR-1 and assess the effect of model ESs on these processes. We found that all three mono-NPs isomers could be readily reduced to their corresponding aminophenols by S. oneidensis MR-1 under anaerobic conditions. CymA, a core component of the Mtr respiratory pathway, performs a dynamic role in these bioreduction, which is highly dependent on the bioreduction kinetics. The exogenous addition of quinones was found to accelerate the mono-NPs bioreduction through interactions with key outer-membrane proteins (e.g., OmcA and MtrC), and all these processes matched well to linear free energy relationships (LFERs). Surprisingly, adding riboflavin did not influence the bioreduction of all three mono-NPs isomers, which may be due to the contribution of OmcA and MtrC to these bioreduction processes and their downregulated expression. This study enhances our understanding of the environmental fate of mono-NPs and their bioconversion processes, providing valuable insights for the bioremediation of nitrophenol-contaminated sites.

Multi-dimensional microfluidic paper-based analytical devices (μPADs) for noninvasive testing: A review of structural design and applications

The rapid emergence of microfluidic paper-based devices as point-of-care testing (POCT) tools for early disease diagnosis and health monitoring, particularly in resource-limited areas, holds immense potential for enhancing healthcare accessibility. Leveraging the numerous advantages of paper, such as capillary-driven flow, porous structure, hydrophilic functional groups, biodegradability, cost-effectiveness, and flexibility, it has become a pivotal choice for microfluidic substrates. The repertoire of microfluidic paper-based devices includes one-dimensional lateral flow assays (1D LFAs), two-dimensional microfluidic paper-based analytical devices (2D μPADs), and three-dimensional (3D) μPADs. In this comprehensive review, we provide and examine crucial information related to paper substrates, design strategies, and detection methods in multi-dimensional microfluidic paper-based devices. We also investigate potential applications of microfluidic paper-based devices for detecting viruses, metabolites and hormones in non-invasive samples such as human saliva, sweat and urine. Additionally, we delve into capillary-driven flow alternative theoretical models of fluids within the paper to provide guidance. Finally, we critically examine the potential for future developments and address challenges for multi-dimensional microfluidic paper-based devices in advancing noninvasive early diagnosis and health monitoring. This article showcases their transformative impact on healthcare, paving the way for enhanced medical services worldwide.

Paper-Based Fluorescent Sensor for Rapid Multi-Channel Detection of Tetracycline Based on Graphene Quantum Dots Coated with Molecularly Imprinted Polymer

In this paper, we developed a paper-based fluorescent sensor using functional composite materials composed of graphene quantum dots (GQDs) coated with molecularly imprinted polymers (MIPs) for the selective detection of tetracycline (TC) in water. GQDs, as eco-friendly fluorophores, were chemically grafted onto the surface of paper fibers. MIPs, serving as the recognition element, were then wrapped around the GQDs via precipitation polymerization using 3-aminopropyltriethoxysilane (APTES) as the functional monomer. Optimal parameters such as quantum dot concentration, grafting time, and elution time were examined to assess the sensor's detection performance. The results revealed that the sensor exhibited a linear response to TC concentrations in the range of 1 to 40 µmol/L, with a limit of detection (LOD) of 0.87 µmol/L. When applied to spiked detection in actual water samples, recoveries ranged from 103.3% to 109.4%. Overall, this paper-based fluorescent sensor (MIPs@GQDs@PAD) shows great potential for portable, multi-channel, and rapid detection of TC in water samples in the future.

Carbon dots-based fluorescent probe for detection of foodborne pathogens and its potential with microfluidics

Concern about food safety triggers demand on rapid, accurate and on-site detection of foodborne pathogens. Among various fluorescent probes for detection, carbon dots (CDs) prepared by carbonization of carbon-rich raw materials show extraordinary performance for their excellent and tailorable photoluminescence property, as well as their facilely gained specificity by surface customization and modification. CDs-based fluorescent probes play a crucial role in many pathogenic bacteria sensing systems. In addition, microfluidic technology with characteristics of portability and functional integration is expected to combine with CDs-based fluorescent probes for point-of-care testing (POCT), which can further enhance the detection property of CDs-based fluorescent probes. Here, this paper reviews CDs-based bacterial detection methods and systems, including the structural modulation of fluorescent probes and pathogenic bacteria detection mechanisms, and describes the potential of combining CDs with microfluidic technology, providing reference for the development of novel rapid detection technology for pathogenic bacteria in food.

Aggregation-induced emission micelle-based sensing array for discrimination of long-chain fatty acids

A sensing array based on aggregation-induced emission micelles was proposed for efficient discrimination of three typical long-chain fatty acids (lauric, palmitic, and stearic acids) and their mixtures.

Elevating nanomaterial optical sensor arrays through the integration of advanced machine learning techniques for enhancing visual inspection of food quality and safety

Food quality and safety problems caused by inefficient control in the food chain have significant implications for human health, social stability, and economic progress and optical sensor arrays (OSAs) can effectively address these challenges. This review aims to summarize the recent applications of nanomaterials-based OSA for food quality and safety visual monitoring, including colourimetric sensor array (CSA) and fluorescent sensor array (FSA). First, the fundamental properties of various advanced nanomaterials, mainly including metal nanoparticles (MNPs) and nanoclusters (MNCs), quantum dots (QDs), upconversion nanoparticles (UCNPs), and others, were described. Besides, the diverse machine learning (ML) and deep learning (DL) methods of high-dimensional data obtained from the responses between different sensing elements and analytes were presented. Moreover, the recent and representative applications in pesticide residues, heavy metal ions, bacterial contamination, antioxidants, flavor matters, and food freshness detection were comprehensively summarized. Finally, the challenges and future perspectives for nanomaterials-based OSAs are discussed. It is believed that with the advancements in artificial intelligence (AI) techniques and integrated technology, nanomaterials-based OSAs are expected to be an intelligent, effective, and rapid tool for food quality assessment and safety control.

Strategy for establishing sensitive fluorescent sensor toward p-nitrophenol integrating magnetic molecularly imprinted materials and carbon dots

In this work, a sensitive fluorescent sensor toward p-nitrophenol (4-NP) integrating magnetic molecularly imprinted materials and carbon dots (CDs) was proposed. Magnetic material and CDs derived from K3 [Fe(CN)6] and glucose were simultaneously obtained through simple one-step hydrothermal process. Introducing of molecularly imprinted materials based magnetic solid phase extraction (MSPE) endowed the constructed fluorescent sensor with higher sensitivity and selectivity. The significant factors affecting the sensitivity of the sensor toward 4-NP were optimized. Good linearity was obtained between fluorescent intensity of CDs and different concentration of 4-NP from 0.08 to 62.5 μg L-1. The sensitivity of constructed sensor was very low with detection limit of 0.02 μg L-1. Reliable applicability was also proved by the well-pleasing recoveries of 94.2-97.8% with different spiked concentrations of 4-NP in real environmental waters.

Bell pepper derived nitrogen-doped carbon dots as a pH-modulated fluorescence switching sensor with high sensitivity for visual sensing of 4-nitrophenol

Recently, converting bio-waste into bio-asset and implementing a portable sensing instrument for pollutant monitoring has been highly desirable and challenging. Herein, biomass-derived nitrogen-doped carbon dots (CDs) are prepared hydrothermally and emit blue fluorescence (470 nm) with a high quantum yield of 23.2%. Significantly, CDs can serve as a pH-modulated fluorescence switching nano-sensor to detect 4-NP from 0.054 to 68 μM with low detection limit (LOD, 54 nM) and limit of quantification (LOQ, 181 nM) based on inner filter effect. Moreover, the satisfactory recovery of 101.8-107.5% is gained in practical sample monitoring. Furthermore, a smartphone-integrated optosensing device with CDs-based film is developed for detecting 4-NP with LOD and LOQ of 0.110 μM and 0.350 μM. Concomitantly, the practicability of this device is further validated in several crop samples with satisfactory recovery rates of 101.6-108.6%. Therefore, this work provides a reliable way and a prospective application for on-site 4-NP monitoring in food.

A molecularly imprinted ratiometric fluorescence sensor based on blue/red carbon quantum dots for the visual determination of thiamethoxam

Neonicotinoids such as thiamethoxam (TMX) were widely used in agricultural production and tended to accumulate in the environment, potentially harming human and ecosystem health. To enable widespread monitoring of TMX residues, it was essential to design a reliable and sensitive detection method. Here, we developed a novel smartphone-enablled molecularly imprinted ratiometric fluorescence sensing system for selective on-site detection of TMX. It was based on blue-emission carbon dots (CDs) wrapped with a molecularly imprinted layer (B-CDs@MIPs), which provided the response signal, while red-emission CDs (R-CDs) served as an internal reference. The fluorescence signal ratio of the sensor increased with the TMX concentration, resulting in an obvious fluorescence color change from red to blue. The sensor exhibited a satisfactory limit of detection (LOD) of 13.5 nM in fluorescence analysis while LOD of 70.1 nM in visual determination. In addition, the sensing system was validated using food and environment samples, exhibiting recoveries from 91.40% to 105.7%, indicating excellent reliability for TMX detection in actual samples. Thus, the sensing system developed in this study offered promising prospects for visual detection of pesticide residues in complex environmental samples.

Breaking the clean room barrier: exploring low-cost alternatives for microfluidic devices

Microfluidics is an interdisciplinary field that encompasses both science and engineering, which aims to design and fabricate devices capable of manipulating extremely low volumes of fluids on a microscale level. The central objective of microfluidics is to provide high precision and accuracy while using minimal reagents and equipment. The benefits of this approach include greater control over experimental conditions, faster analysis, and improved experimental reproducibility. Microfluidic devices, also known as labs-on-a-chip (LOCs), have emerged as potential instruments for optimizing operations and decreasing costs in various of industries, including pharmaceutical, medical, food, and cosmetics. However, the high price of conventional prototypes for LOCs devices, generated in clean room facilities, has increased the demand for inexpensive alternatives. Polymers, paper, and hydrogels are some of the materials that can be utilized to create the inexpensive microfluidic devices covered in this article. In addition, we highlighted different manufacturing techniques, such as soft lithography, laser plotting, and 3D printing, that are suitable for creating LOCs. The selection of materials and fabrication techniques will depend on the specific requirements and applications of each individual LOC. This article aims to provide a comprehensive overview of the numerous alternatives for the development of low-cost LOCs to service industries such as pharmaceuticals, chemicals, food, and biomedicine.

Threaded 3D microfluidic paper analytical device-based ratiometric fluorescent sensor for background-free and visual detection of organophosphorus pesticides

With the increasing concerns of food safety and environmental protection, it is desirable to develop reliable, effective, and portable sensors for detection of organophosphorus pesticides (OPs). Here, a cascade reaction system integrated with threaded 3D microfluidic paper analytical device (3D μPAD) was firstly developed for background-free and visual detection of OPs in agricultural samples. Butyrylcholinesterase (BChE) hydrolyzed acetylcholine into thiocholine (TCh), which reduced MnO₂ nanosheets into Mn²⁺. With addition of OPs, BChE activity was irreversibly inhibited, and the generation of TCh and the reduction of MnO₂ nanosheets were prevented. Then the remaining MnO₂ nanosheets oxidized o-phenylenediamine into 2,3-diaminophenazine with yellow-emission fluorescence, which quenched the fluorescence intensity of red-emission carbon dots (RCDs) via inner-filter effect. Based on above mechanism, a ratiometric fluorescent system was established for OPs detection. Threaded 3D μPAD consisted of 4 layers, which allowed to load and/or add reagents to trigger the cascade reaction system for OPs detection. The fluorescent images presented distinguishable color variations from red to yellow with dichlorvos concentrations ranging from 2.5 to 120 μg L^-1, and the limit of detection was 1.0 μg L^-1. In the practical samples testing, threaded 3D μPAD can eliminate background influence on fluorescent signal for OPs detection. Threaded 3D μPAD integrated with ratiometric sensing platform has merits of accuracy response, facile operation, and background-free detection, which supplies a new alternative approach for on-site pesticide detection.

Current Progress of Ratiometric Fluorescence Sensors Based on Carbon Dots in Foodborne Contaminant Detection

Carbon dots (CDs) are widely used in the detection of foodborne contaminants because of their biocompatibility, photoluminescence stability, and ease of chemical modification. In order to solve the interference problem of complexity in food matrices, the development of ratiometric fluorescence sensors shows great prospects. In this review, the progress of ratiometric fluorescence sensors based on CDs in foodborne contaminant detection in recent years will be summarized, focusing on the functionalized modification of CDs, the fluorescence sensing mechanism, the types of ratiometric fluorescence sensors, and the application of portable devices. In addition, the outlook on the development of the field will be presented, with the development of smartphone applications and related software helping to better enable the on-site detection of foodborne contaminants to ensure food safety and human health.

Paper-Based Molecular-Imprinting Technology and Its Application

Paper-based analytical devices (PADs) are highly effective tools due to their low cost, portability, low reagent accumulation, and ease of use. Molecularly imprinted polymers (MIP) are also extensively used as biomimetic receptors and specific adsorption materials for capturing target analytes in various complex matrices due to their excellent recognition ability and structural stability. The integration of MIP and PADs (MIP-PADs) realizes the rapid, convenient, and low-cost application of molecular-imprinting analysis technology. This review introduces the characteristics of MIP-PAD technology and discusses its application in the fields of on-site environmental analysis, food-safety monitoring, point-of-care detection, biomarker detection, and exposure assessment. The problems and future development of MIP-PAD technology in practical application are also prospected.