Dan Li

Bio: Dan Li is an academic researcher from Shanghai Institute of Technology. The author has contributed to research in topics: Quantum dot & Nanoprobe. The author has an hindex of 12, co-authored 31 publications receiving 433 citations.

Headspace-Sampling Paper-Based Analytical Device for Colorimetric/Surface-Enhanced Raman Scattering Dual Sensing of Sulfur Dioxide in Wine

Abstract: This study demonstrates a novel strategy for colorimetric/surface-enhanced Raman scattering (SERS) dual-mode sensing of sulfur dioxide (SO2) by coupling headspace sampling (HS) with paper-based analytical device (PAD). The smart and multifunctional PAD is fabricated with a vacuum filtration method in which 4-mercaptopyridine (Mpy)-modified gold nanorods (GNRs)-reduced graphene oxide (rGO) hybrids (rGO/MPy-GNRs), anhydrous methanol, and starch-iodine complex are immobilized into cellulose-based filter papers. The resultant PAD exhibits a deep-blue color with a strong absorption peak at 600 nm due to the formation of an intermolecular charge-transfer complex between starch and iodine. However, the addition of SO2 induces the Karl Fischer reaction, resulting in the decrease of color and increase of SERS signals. Therefore, the PAD can be used not only as a naked-eye indicator of SO2 changed from blue to colorless but also as a highly sensitive SERS substrates because of the SO2-triggered conversion of Mpy to...

Facile in situ synthesis of core–shell MOF@Ag nanoparticle composites on screen-printed electrodes for ultrasensitive SERS detection of polycyclic aromatic hydrocarbons

Abstract: This paper reports the fabrication of a highly sensitive and reusable substrate for surface-enhanced Raman scattering (SERS) analysis. Core–shell metal–organic framework (MOF; HKUST-1)@Ag nanoparticles (NPs) are prepared on a screen-printed carbon electrode (SPCE) via in situ electrodeposition. The morphology and Ag coverage of core–shell structures can be easily controlled by electrodeposition potential and time without substrate motion. The HKUST-1(Cu)@Ag composites combine abundant SERS “hot spots” among the high-density Ag NPs and the excellent adsorption performance of the MOF, resulting in effective pre-concentration of analytes in close proximity to these “hot spots” and enhancement of SERS sensitivity. The optimized polyhedral HKUST-1@Ag structures exhibit high SERS activity for detecting 4-aminothiophenol at a concentration as low as 5 × 10−10 M. More importantly, the polyhedral HKUST-1@Ag composites provide high sensitivity for detection of polycyclic aromatic hydrocarbons (PAHs) while preserving the cyclability and selectivity required for reliable quantitative analysis. The method is effective over a wide range of PAH concentrations (0.5 nM to 0.5 M), with detection limits as low as hundreds of pM. This study offers a new method to tailor the structure of MOF-based SERS substrates for on-site screening or point-of-care applications.

On-site preconcentration of pesticide residues in a drop of seawater by using electrokinetic trapping, and their determination by surface-enhanced Raman scattering

Abstract: The authors have developed a method for simultaneous quantification of several charged pesticides (as shown for amitrole, simazine, trichlorfon and bisultap). It is based on the use of a reduced graphene oxide-modified screen-printed electrode (RGO-SPE) and combines electrokinetic trapping (EKT) and surface-enhanced Raman scattering (SERS). When a 50 μL droplet containing negatively charged RGO and positively charged gold nanorods is placed on the SPE, the RGO and gold nanorods are selectively attracted on the surface of the SPE during EKT. This leads to the formation of sandwich-type hybrid substrates. The resulting substrates also contain Raman "hot spots" among the high-density gold nanorods. This, along with the excellent adsorption performance of RGO, makes it an excellent SERS substrate for on-site detection of the charged pesticides. The method is highly reproducible and long-term stable. The spot-to-spot variation of the intensity of the SERS is <15%, and the performance of SERS activity is maintained over a period of 6 weeks. The method works over a wide range of concentrations (0.5 nM to 4 μM) for charged pesticides under optimal conditions, with a sub-nanomolar detection limit (at a signal to noise ratio of 3). The EKT-SERS method requires only microliter volumes and takes only minutes for completion. Therefore, the method provides high sensitivity for detection while preserving the selectivity and stability required for reliable quantitative analysis. Graphical abstract A method combining electrokinetic trapping and SERS can be used for simultaneous detection of charged pesticides in a drop of seawater.

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

Abstract: 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.

Supramolecular Luminescent Sensors

Abstract: There is great need for stand-alone luminescence-based chemosensors that exemplify selectivity, sensitivity, and applicability and that overcome the challenges that arise from complex, real-world media. Discussed herein are recent developments toward these goals in the field of supramolecular luminescent chemosensors, including macrocycles, polymers, and nanomaterials. Specific focus is placed on the development of new macrocycle hosts since 2010, coupled with considerations of the underlying principles of supramolecular chemistry as well as analytes of interest and common luminophores. State-of-the-art developments in the fields of polymer and nanomaterial sensors are also examined, and some remaining unsolved challenges in the area of chemosensors are discussed.

Food colorants: Challenges, opportunities and current desires of agro-industries to ensure consumer expectations and regulatory practices

Abstract: Background Worldwide consumers seek most delightful and appealing foodstuffs, at the same time they require safer, more nutritious and healthier products. Color is one of the most important organoleptic attributes that directly affects consumers' acceptance and food selection. Scope and approach The present report aims to provide an extensive approach to the field of food (natural/synthetic) colorants, namely those who are currently allowed with established acceptable daily intake (ADI). It also describes the biotechnological and industrial techniques that have been used to optimize food attractiveness, shelf life and color stability, as well as the general trends and future perspectives of food science and technology in the topic of food colorants. Key findings and conclusions Synthetic food colorants were largely used, but have been progressively substituted by those obtained from natural origins. Numerous side effects and toxicity, at both medium and long-terms, allergic reactions, behavioral and neurocognitive effects have been related with their use. Otherwise, naturally-derived food colorants seem to provide high quality, efficiency and organoleptic properties, and also play a contributive role as health promoters. Anthocyanins, carotenoids, phenolic compounds, beet derivatives, annatto and some curcuminoids are among the most commonly used, while strict regulatory practices have been applied looking for food quality assurance.

Optical Sensing and Imaging of pH Values: Spectroscopies, Materials, and Applications

Abstract: This is the first comprehensive review on methods and materials for use in optical sensing of pH values and on applications of such sensors. The Review starts with an introduction that contains subsections on the definition of the pH value, a brief look back on optical methods for sensing of pH, on the effects of ionic strength on pH values and pKa values, on the selectivity, sensitivity, precision, dynamic ranges, and temperature dependence of such sensors. Commonly used optical sensing schemes are covered in a next main chapter, with subsections on methods based on absorptiometry, reflectometry, luminescence, refractive index, surface plasmon resonance, photonic crystals, turbidity, mechanical displacement, interferometry, and solvatochromism. This is followed by sections on absorptiometric and luminescent molecular probes for use pH in sensors. Further large sections cover polymeric hosts and supports, and methods for immobilization of indicator dyes. Further and more specific sections summarize the state of the art in materials with dual functionality (indicator and host), nanomaterials, sensors based on upconversion and 2-photon absorption, multiparameter sensors, imaging, and sensors for extreme pH values. A chapter on the many sensing formats has subsections on planar, fiber optic, evanescent wave, refractive index, surface plasmon resonance and holography based sensor designs, and on distributed sensing. Another section summarizes selected applications in areas, such as medicine, biology, oceanography, bioprocess monitoring, corrosion studies, on the use of pH sensors as transducers in biosensors and chemical sensors, and their integration into flow-injection analyzers, microfluidic devices, and lab-on-a-chip systems. An extra section is devoted to current challenges, with subsections on challenges of general nature and those of specific nature. A concluding section gives an outlook on potential future trends and perspectives.

Recent Advances in Electrochemical Sensors for Detecting Toxic Gases: NO₂, SO₂ and H₂S.

Abstract: Toxic gases, such as NOx, SOx, H2S and other S-containing gases, cause numerous harmful effects on human health even at very low gas concentrations. Reliable detection of various gases in low concentration is mandatory in the fields such as industrial plants, environmental monitoring, air quality assurance, automotive technologies and so on. In this paper, the recent advances in electrochemical sensors for toxic gas detections were reviewed and summarized with a focus on NO2, SO2 and H2S gas sensors. The recent progress of the detection of each of these toxic gases was categorized by the highly explored sensing materials over the past few decades. The important sensing performance parameters like sensitivity/response, response and recovery times at certain gas concentration and operating temperature for different sensor materials and structures have been summarized and tabulated to provide a thorough performance comparison. A novel metric, sensitivity per ppm/response time ratio has been calculated for each sensor in order to compare the overall sensing performance on the same reference. It is found that hybrid materials-based sensors exhibit the highest average ratio for NO2 gas sensing, whereas GaN and metal-oxide based sensors possess the highest ratio for SO2 and H2S gas sensing, respectively. Recently, significant research efforts have been made exploring new sensor materials, such as graphene and its derivatives, transition metal dichalcogenides (TMDs), GaN, metal-metal oxide nanostructures, solid electrolytes and organic materials to detect the above-mentioned toxic gases. In addition, the contemporary progress in SO2 gas sensors based on zeolite and paper and H2S gas sensors based on colorimetric and metal-organic framework (MOF) structures have also been reviewed. Finally, this work reviewed the recent first principle studies on the interaction between gas molecules and novel promising materials like arsenene, borophene, blue phosphorene, GeSe monolayer and germanene. The goal is to understand the surface interaction mechanism.

Potential Utility of Metal–Organic Framework-Based Platform for Sensing Pesticides

Abstract: The progress in modern agricultural practices could not have been realized without the large-scale contribution of assorted pesticides (e.g., organophosphates and nonorganophosphates). Precise tracking of these chemicals has become very important for safeguarding the environment and food resources owing to their very high toxicity. Hence, the development of sensitive and convenient sensors for the on-site detection of pesticides is imperative to overcome practical limitations encountered in conventional methodologies, which require skilled manpower at the expense of high cost and low portability. In this regard, the role of novel, advanced functional materials such as metal–organic frameworks (MOFs) has drawn great interest as an alternative for conventional sensory systems because of their numerous advantages over other nanomaterials. This review was organized to address the recent advances in applications of MOFs for sensing various pesticides because of their tailorable optical and electrical character...