Microfluidic paper-based analytical devices (μPADs) have experienced rapid growth over the past decade due to their simple design, low cost, minimal sample requirement, and good sensitivity, selectivity and accuracy. While designed originally for point-of-care medical diagnostics, biological, and food safety applications, μPADs are now used increasingly for environmental monitoring purposes. This review provides a detailed overview of the μPADs developed over the past ten years for the environmental analysis of soil, air, ecology (pesticides) and river water. The review commences by introducing the fabrication techniques and detection methods used in μPAD technology. A detailed description of the main μPAD frameworks proposed in the past decade for environmental monitoring is then provided. The review concludes by examining the challenges facing μPADs for environmental monitoring and identifying probable avenues of future research.

Microfluidic paper-based analytical devices for environmental analysis of soil, air, ecology and river water

This study introduces an innovative procedure for the development of a molecularly imprinted electrochemical sensor for ultra-sensitive and selective detection of patulin. Firstly, the surface of a glassy carbon electrode (GCE) was decorated by nitrogen doped graphene quantum dots (N-GQDs) and AuNPs-functionalized Cu-metal organic framework (Au@Cu-MOF) and then a layer of molecularly imprinted polymer (MIP) was grown on Au@Cu-MOF/N-GQDs/GCE by electropolymerization. Electrochemical techniques were used to characterize and study the electrochemical behavior of the MIP/Au@Cu-MOF/N-GQDs/GCE, which exhibited a stable reference peak of Au@Cu-MOF at −0.11 V after elution of patulin molecules. This peak current density decreased with rebinding of patulin molecules therefore it was considered as indicator signal. The designed MIP sensor presented a wide linear range from 0.001 to 70.0 ng mL−1, and a low detection limit (0.0007 ng mL−1). This newly developed method based on the synergistic effects of N-GQDs and Au@Cu-MOF combined with MIP technique offered outstanding selectivity, sensitivity, stability, and reproducibility. The good accuracy (recovery%, 97.6–99.4) and high precision (RSD%, 1.23–4.61) of this sensing system for analysis of apple juices proved the high potential of it for rapid and low cost determination of patulin compared to chromatographic methods.

Ultra-sensitive molecularly imprinted electrochemical sensor for patulin detection based on a novel assembling strategy using Au@Cu-MOF/N-GQDs

Surface-enhanced Raman spectroscopy (SERS) is a powerful analytical technique, which allows quantitative detection of chemical species with molecular specificity and single-molecule sensitivity. These useful properties can be further combined with portable Raman spectrometers which allow SERS to be potentially employed at the point-of-care. As a result, SERS has found a wide range of potential applications in both real-life chemical analysis and fundamental mechanistic studies. Despite these advantages, true applications of SERS have been limited due to its high cost, which arises mainly from the fact that SERS relies on expensive single-use Ag/Au enhancing substrates suitable only for the analysis of pure samples. A viable approach to address this issue is to develop multifunctional SERS substrates, which in addition to providing Raman signal enhancement, is armed with other practical functionalities that simplifies the analysis and/or allows the substrate to be regenerated for repeated use. This review gives an account of the recent progress in the fabrication of multi-functional SERS substrates, namely flexible, separation-enhancement-in-one, calibration-enhancement-in-one and regeneration-enhancement-in-one substrates. Specific focus is placed on summarizing and discussing the most widely used strategies to incorporate each type of functionality and their respective advantages and drawbacks. Finally, we present our perspectives on the future challenges and potential opportunities in the development of smart multifunctional SERS sensors for achieving sustainable and wide-spread application of SERS.

/pdf/towards-practical-and-sustainable-sers-a-review-of-recent-7al68aiuj1.pdf

Towards practical and sustainable SERS: a review of recent developments in the construction of multifunctional enhancing substrates

Food safety issues have recently attracted public concern. The deleterious effects of compromised food safety on health have rendered food safety analysis an approach of paramount importance. While conventional techniques such as high-performance liquid chromatography and mass spectrometry have traditionally been utilized for the detection of food contaminants, they are relatively expensive, time-consuming and labor intensive, impeding their use for point-of-care (POC) applications. In addition, accessibility of these tests is limited in developing countries where food-related illnesses are prevalent. There is, therefore, an urgent need to develop simple and robust diagnostic POC devices. POC devices, including paper- and chip-based devices, are typically rapid, cost-effective and user-friendly, offering a tremendous potential for rapid food safety analysis at POC settings. Herein, we discuss the most recent advances in the development of emerging POC devices for food safety analysis. We first provide an overview of common food safety issues and the existing techniques for detecting food contaminants such as foodborne pathogens, chemicals, allergens, and toxins. The importance of rapid food safety analysis along with the beneficial use of miniaturized POC devices are subsequently reviewed. Finally, the existing challenges and future perspectives of developing the miniaturized POC devices for food safety monitoring are briefly discussed.

Emerging Point-of-care Technologies for Food Safety Analysis.

Background Food safety issues leading to severe healthy, economic and even social problems and detection of food contaminants has been attracting remarkable attention in recent decades Surface-enhanced Raman scattering (SERS) is one of the most promising techniques to enable detecting contaminants at trace levels Besides, with the emergence of global resource shortages and environmental problems, there is a growing demand for environmentally friendly and renewable resources As a sustainable and biodegradable raw material, cellulose has aroused great interest and stimulated researchers to develop cellulose-based SERS substrates with novel functions Scope and approach The review focuses on the utilizing of cellulosic materials for the design and preparation of various SERS substrates, including cellulose-papers, cellulose fabrics (CFs) and membranes, cellulose nanofibrils (CNFs), bacterial cellulose (BC), nanocrystalline cellulose (NCC), and surface-modified cellulose The applications, challenges and potential solutions of these cellulose-based substrates in food safety detection are also presented, proposed and evaluated Key findings and conclusions For the complexity and diversity of multitudinous food systems, multiple approaches have been successfully employed to manufacture cellulose-based SERS substrates Various types of cellulose with diverse morphology and mechanical properties make them customizable and integratable with multiple technologies in certain realistic applications The explorations of SERS detections displaying excellent performances especially for the complex system/surface analysis with the capability of extraction, swabbing, transferring and concentrating target molecules from complexing food systems The widespread application and prominent performance demonstrating the huge potential for cellulose-based materials to realize commercially viable, sustainable, flexible and green substrates in the near future

Multifunctional cellulose based substrates for SERS smart sensing: Principles, applications and emerging trends for food safety detection

Ideal SERS substrates and rapid sampling are crucial for on-site detection of pesticide residues. In this work, silver nanoparticles and graphene oxide were successfully prepared on cellulose paper (Ag NPs/GO paper) using a screen printing technique. The screen printing ink containing graphene oxide and silver nanoparticles was orderly printed onto cellulose paper substrates by controlling the printing cycles to fabricate controllable SERS substrates in large batches for the detection of pesticide residues. It was found that for up to four cycles, the SERS effect increased with the number of Ag NP printing cycles and no obvious change was observed. The prepared Ag NPs/GO paper may exhibit a high enrichment ability due to the π–π stacking and electrostatic interactions of GO toward pesticide molecules. The results suggest that the high density of Ag NPs/GO on the prepared paper is enough for ultrasensitive SERS detection of thiram, thiabendazole and methyl parathion in complex surfaces with a low limit of detection of 0.26 ng cm−2, 28 ng cm−2, and 7.4 ng cm−2, which are much lower than the maximal residue limits in fruit prescribed by the U.S. Environmental Protection Agency. Thus, the sensitive SERS detection of pesticide residues based on Ag NPs/GO paper offers great potential for its practical application in environmental analysis and food safety.

Rapid and sensitive on-site detection of pesticide residues in fruits and vegetables using screen-printed paper-based SERS swabs

Fluorescent magnetic chitosan-based hydrogel incorporating Amino-Functionalized Fe3O4 and cellulose nanofibers modified with carbon dots for adsorption and detection of Cr (VI)

Negatively charged molybdate mediated nitrogen-doped graphene quantum dots as a fluorescence turn on probe for phosphate ion in aqueous media and living cells.

Since hydrogen peroxide plays an important role in various fields, a facile, simple, highly selective, and stable analytic method for H2O2 is desirable. Semiconductor quantum dots (QDs) have acted as a potential alternative for organic fluorophores in fluorescence analytical fields due to their superior optical properties. Herein, we report hydrophilic p-hydroxy thiophenol (p-HTP) coated CdSe/ZnS QDs (denoted as p-HTP-QDs) acting as a selective fluorescence ‘turn-on’ probe for H2O2 in aqueous media. The obtained p-HTP-QD probe exhibits weak fluorescence, which stems from hole transfer from the QDs to p-HTP. The presence of H2O2 induces an oxidative structural transformation of p-HTP in p-HTP-QDs from a phenol structure to an α-hydroxy ketone derivative, which extremely reduces the driving force for hole transfer. Thus, the QDs photoluminescence (PL) was re-switched on. Under optimized conditions, an excellent linear relationship between fluorescence response and H2O2 concentration could be produced with a linear range from 0.309 to 4.900 mM. The limit of detection of this probe was found to be 0.135 mM. Moreover, the present probe exhibited a high selectivity of H2O2 over other reactive oxygen species/reactive nitrogen species (ROS/RNS) and was successfully used in the detection of H2O2 in real water samples.

para-Hydroxy Thiophenol-Coated CdSe/ZnS Quantum Dots as a Turn-On Fluorescent Probe for H2O2 Detection in Aqueous Media

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Rapid and sensitive on-site detection of pesticide residues in fruits and vegetables using screen-printed paper-based SERS swabs

Fluorescent magnetic chitosan-based hydrogel incorporating Amino-Functionalized Fe3O4 and cellulose nanofibers modified with carbon dots for adsorption and detection of Cr (VI)

Negatively charged molybdate mediated nitrogen-doped graphene quantum dots as a fluorescence turn on probe for phosphate ion in aqueous media and living cells.

para-Hydroxy Thiophenol-Coated CdSe/ZnS Quantum Dots as a Turn-On Fluorescent Probe for H2O2 Detection in Aqueous Media