Enhanced oxidase-mimic constructed by luminescent carbon dots loaded on MIL-53(Fe)-NO2 for dual-mode detection of gallic acid and biothiols in food and humans.

Monitoring of gallic acid (GA) in food and biothiols in humans is crucial for body health. Nanozyme-mediated colorimetric strategy for evaluating them has been widely applied nowadays, however, the inferior efficient and susceptible single-signal recognition limit its further application. Herein, a sensitive biosensor was first constructed for bimodal detection of GA and biothiols based on CDs@MIL-53(Fe)-NO2, prepared through a facile and time-saving microwave treatment. Benefiting from the excellent fluorescent and electron transfer properties of CDs, CDs@MIL-53(Fe)-NO2 exhibited significant enhanced blue fluorescence and oxidase-like activity, which could oxide colorless 3,3',5,5'-tetramethylbenzidine without H2O2, and the blue product could quench the fluorescence of composite. The dual-mode assay based on such bifunctional nanozyme showed an extremely sensitivity towards GA/l-cysteine/homocysteine with the detection limit of 62/65/124 nM and 17/16/27 nM in colorimetric/fluorescent modes, respectively. The practicability in real samples and portability based on a smartphone of the analysis has been investigated with reliable results.

Magnetic-fluorescent immunosensing platform applying AuNPs heterogeneous MIL-53(Al) composite for efficient detection of zearalenone.

Rapid, sensitive, specific and stable detection of mycotoxin in food remains an extremely crucial issue. Herein, a magnetic-fluorescent immunosensing platform for the detection of zearalenone (ZEN) was proposed. The platform utilized Au nanoparticles (AuNPs) heterogeneous fluorescent metal-organic framework (MIL-53(Al)@AuNPs) labeled with ZEN-bovine serum albumin (ZEN-BSA) as signal probe and ZEN mono-antibodies coupled with magnetic NPs (MNPs-mAbs) as capture probe. Specifically, the heterogenization of AuNPs on the MIL-53(Al) surface improved its biocompatibility, and facilitated the loading of ZEN-BSA conjugates. The MNPs-mAbs could rapidly capture the target ZEN, simplify the immunoassay process and further improve the detection efficiency. The established competitive magnetic-fluorescent immunosensing platform had a wider linear response to ZEN in the range of 0.001-100 ng/mL with a lower limit of detection (LOD) at 0.0035 ng/mL, and could finish the whole detection process within 20 min, showing great potential for rapid and sensitive detection of food contaminants.

Synthesis of polymer dots as fluorescent nanoprobe for the detection of Ponceau 4R, an additive color abuse in food.

Abusing organic dyes in industrial food products is an important issue in many countries. Rapid chemical sensing of these compounds can be of great importance during the industrial life of humans. In this work, we synthesized a new fluorescent polymer dot and successfully applied it as an optical probe for the detection of red color abuse in foodstuffs. Ponceau 4R is a red organic dye additive that is used in some foodstuffs such as tomato sauces or pastes. It is too hazardous to human health. Detection of such abusage is challenging. The development of π-conjugated polymer dots having a bright emission band at visible can be a promising probe for the detection of food color additives. A variety of methods and monomers were previously used for their synthesis. Here, the Suzuki Coupling method was employed. The limit of detection (LOD) of the method was obtained 16 nmol L-1 for the detection of Ponceau 4R.

Super-Resolution Microscopy of the Bacterial Cell Wall Labeled by Fluorescent D-Amino Acids.

Fluorescent D-amino acids (FDAAs) enable in situ visualization of bacterial cell wall synthesis via their incorporation into peptidoglycan (PG) crosslinks. When combined with super-resolution microscopy, FDAAs allow the details of cell wall synthesis to be resolved beyond the diffraction limit of visible light. Here, we describe using the super-resolution method of single-molecule localization microscopy (SMLM) in conjunction with two newly synthesized FDAAs (sCy5DA and sCy5DL_amide) to resolve bacterial PG at the nanoscale in a variety of species, including Gram-negative, Gram-positive, and mycobacteria.

A ratiometric fluorescence platform for on-site screening meat freshness.

Meat freshness is related to food safety and human health. Developing a simple and effective method for on-site detection of meat freshness is essential to ensure food safety. This study aimed to explore a ratiometric fluorescence platform for on-site screening of meat freshness. We synthesized a series of benzothiazole-based fluorescent compounds (BM, BHM and BTH), each with different recognition groups for detecting meat freshness biomarkers cadaverine (Cad) and putrescine (Pte). The optimized 2-(2'-hydroxyphenyl-3-aldehyde-5-1,3-indanedione) benzothiazole (BTH) demonstrated a noticeable color and fluorescence change, a fast response (<15 min), and high selectivity and sensitivity (LOD = 70 nM) to Cad. Portable test strips based on BTH were prepared for rapid visual detection of meat freshness, which exhibited visible color and fluorescen color changes to Cad and Pte. Furthermore, a portable smartphone-based fluorescence device integrated with a self-programmed Python program was fabricated and used on-site to monitor Cad and Pte within 5 min. The BTH-loaded portable test strips were successfully employed as low-cost, high-contrast, fast-response, and smartphone-adaptable fluorescent labels for detecting Cad and Pte in meat samples under different temperatures (25 °C, 4 °C, and -20 °C). This enabled consumers and food supply chain stakeholders to quickly and visually monitor the meat freshness in real beef, chicken, and pork products.

Upgraded ß-cyclodextrin-based broad-spectrum adsorbents with enhanced antibacterial property for high-efficient dyeing wastewater remediation.

The dyeing wastewater contains amounts of refractory organic compounds, and severely endangers the ecosystem and human health. To alleviate this problem, in this study, the low-cost broad-spectrum nano-adsorbent (denoted as CD/CA-g-CS) with strong antibacterial activity has been synthesized by chemical binding of ß-cyclodextrin (ß-CD) with chitosan (CS) and citric acid (CA) for high-efficient dyes scavenger. Taking advantage of the extraordinary water insolubility, porous nature and abundant surface groups, the synthesized CD/CA-g-CS outperforms the previously reported adsorbents in terms of adsorption performance. The CD/CA-g-CS exhibits ultrahigh adsorption capacities of 801.66, 770.50 and 946.66 mg/g, respectively mg/g for the cationic dyes of malachite green (MG), basic red (BR) and methylene blue (MB), respectively, while 389.64, 619.60 and 429.22 mg/g for the anionic dyes of acid blue (AB), acid red (AR) and acid yellow (AY), respectively. The chemical monolayer absorption is further demonstrated by the analysis based on the pseudo-second-order adsorption kinetics and Langmuir isotherm models. The regenerable CD/CA-g-CS not only performs well in one-step removal of the mixed dyes in the simulated sewage, but also exhibits superior performance in purifying real industrial wastewater. Moreover, CD/CA-g-CS endowed with antibacterial activity leads to an inhibition rate of over 99.99 % for E. coli. The newly developed CD/CA-g-CS adsorbents are highly promising for high-efficient dyeing wastewater remediation.

Alkaline phosphatase triggered gold nanoclusters turn-on fluorescence immunoassay for detection of Ochratoxin A.

Ochratoxin A (OTA) is a highly toxic mycotoxin which can cause a variety of diseases. Sensitive detection of OTA is significant for food safety. Herein, a feasible and sensitive immunoassay was established for OTA detection by alkaline phosphatase (ALP) triggered gold nanoclusters (AuNCs) turn-on fluorescence. The fluorescence of the AuNCs can be quenched by Cr6+ induced aggregation of AuNCs and the fluorescence resonance energy transfer (FRET) between AuNCs and Cr6+. Under the catalytic action of ALP-labelled IgG (IgG-ALP), the ascorbic acid 2-phosphate (AA2P) was hydrolyzed to ascorbic acid (AA) for the reducing of Cr6+ to Cr3+. As a result, the degrees of AuNCs aggregation and FRET were weakened and the fluorescence of AuNCs was turned on. The amount of OTA in the sample was negatively correlated with the amount of IgG-ALP captured by anti-OTA monoclonal antibody (McAb) in the microplate. In optimal conditions, the turn-on fluorescence immunoassay had a good linear range of 6.25-100 ng/mL, and the detection limit was 0.693 ng/mL. The recoveries of OTA from corn were 95.89%-101.08% for the fluorescence immunoassay. This work provided a feasible, sensitive and good selectivity fluorescence method for OTA detection.

Recent advances in electrochemical sensors based on nanomaterials for detection of red dyes in food products: A review.

Red dyes as Allura Red (E129), Amaranth (E124), Ponceau 4R (E123), Erythrosine (E127) and Carmoisine (E122), are very popular food additives due to their stability, low cost, and minimal microbial contamination. Despite these advantages, their consumption may result in asthma, hyperactivity, carcinogenic effects, etc depending on the uptake and age. Therefore, the United States Food and Drug Administration (FDA) and European Food Safety Authority (EFSA) have managed the permissions of allowed daily intake (ADI) for consumption levels of these dyes to be 0.01-7.0 mg/kg to assure foodstuffs consumer's safety and avoid their adverse effects. Yet, many countries as Japan and USA have prohibited their use in food and drinks to reduce their possible health risks. Based on the above concentration ranges, highly sensitive and selective detection techniques are required, accordingly, the application of electrochemical sensors for the analysis of these dyes in food samples is very promising due to their superior sensitivity and selectivity, low cost and rapid response compared to traditional spectrophotometric or chromatographic methods. Also, they can be miniaturized, portable and require no complicated sampling or preparation procedures, besides being ecofriendly which allows their commercialization for public consumers in fast detection kits. In this review, the role of nanomaterials such as: carbon-based, transition metal oxides, metal organic frameworks, ionic liquids and others in enhancing the detection properties of modified electrochemical sensors for red dyes will be evaluated in terms of the type of nanomaterial applied, tested food samples and their impact on the evaluation of foodstuffs quality.

Teíchophoresis-enabled electrokinetic sample preparation and detection of calcium in natural plant samples.

We present a novel upstream electrokinetic sample preparation and liquid interfacial microfluidic method to pre-concentrate, detect and quantify the concentration of a charged species, such as calcium, from a natural plant sample. We employ a new electrokinetic phenomenon, termed as "Teíchophoresis" (TPE) to preconcentrate sample calcium ions (up to a 20X increase) against a conductive wall. Using microfluidic flow, we then continuously transport the pre-concentrated calcium to a hydrodynamically streamed interfacial sensing zone where we utilize the model fluorescent chelation reaction between calcium and Calcium Green-1 (CG1) to fluorescently quantify the calcium concentration. Using a combination of finite element analysis and finite difference numerical modelling, we model the kinetics of the CG1-calcium interfacial binding and predictably validate our TPE-driven concentration results. Finally, we demonstrate the applicability of our device for real world samples by determining the calcium concentration in a tree bark extract acquired from a southern live oak and confirm our concentration results using ICP-MS.

A luminescent MOF-based nonenzymatic probe for colorimetric/photothermal/fluorescence triple-mode assay of uric acid in body fluids.

Monitoring the levels of uric acid (UA) in body fluids is of great significance in the clinical diagnosis and therapy of related diseases. Herein, a novel nanocomposite R6G@Fe-MOF based nonenzymatic probe is presented to provide a ratiometric fluorescent, colorimetric, and photothermal triple read-out signal for the visual, sensitive, and convenient assay of UA. The framework structure of the in situ encapsulated R6G@Fe-MOF is found to decompose upon the addition of UA, resulting in the reduction of Fe3+ to Fe2+. This reduction will lead to a rapid increase in fluorescence emission (FL) at 430 nm. Simultaneously, the FL at 573 nm will decrease remarkably due to the inner filter effect (IFE) between UA and R6G@Fe-MOF. Furthermore, the reaction of the generated Fe2+ with potassium ferricyanide (K3 [Fe(CN)6]) can in situ generate Prussian blue (PBNPs) with outstanding color and photothermal properties, which allow for easy colorimetric and photothermal signal readout. The detection limits (LOD) for the colorimetric, fluorometric and photothermal detection are low at 1.68 µM, 0.236 µM, and 1.32 µM respectively. Ultimately, it is successfully employed to determine UA in urine, serum, and saliva, yielding satisfactory results. The constructed R6G@Fe-MOF sensor provides a simple, sensitive, and accurate determination of UA that can be tailored to meet the needs of various applications, and also provides new perspectives for the design and development of versatile sensors for diverse uses.

Magnetically actuated microfluidic chip combined with a G-quadruplex DNAzyme-based fluorescent/colorimetric sensor for the dual-mode detection of ochratoxin A in wheat.

In this work, a portable fluorescent/colorimetric sensor based on G-quadruplex DNAzyme was constructed to achieve rapid and dual-mode detection of ochratoxin A (OTA) in wheat. OTA aptamers coupled with magnetic beads (MBs) can self-assemble with two segments of DNA and hemin to form a G-quadruplex DNAzyme structure that can catalyze the oxidation of Amplex Red (ADHP) with H2O2, making the solution red and producing strong fluorescence in solution. However, in the presence of OTA, the structure of the G-quadruplex DNAzyme was damaged, resulting in reduced catalytic activity. According to the principle of detection, a magnet-controlled chip integrating the reaction, washing, and detection was designed in this study. Shuttling the MB-DNAzyme probes onto a magnetically controlled chip considerably reduced the background signal and improved the detection efficiency and sensitivity. In addition, a portable fluorescence and colorimetric detection platform was built for on-site OTA detection.

Graphene oxide mediated CdSe quantum dots fluorescent aptasensor for high sensitivity detection of fluoroquinolones.

In view of the urgent need for fluoroquinolones contamination detection in the fields of food safety, a novel aptasensor based on the fluorescence quenching property of graphene oxide (GO) and the fluorescence characteristic of cadmium selenide quantum dots (CdSe QDs) was developed for fluoroquinolones highly sensitive detection in this work. The CdSe QDs with carboxyl-rich surface were synthesized successfully and fluoresced at 525 nm under the optimal excitation light of 366 nm. Based on the hydrophobic and π-π stacking between GO and aptamer, aptamer labeled by CdSe QDs fluorescence (CdSe QDs-apt) were adsorbed by GO and the fluorescence of CdSe QDs was quenched. After the aptamer combined specifically with fluoroquinolones, greater specific force lead to the desorption of CdSe QDs-apt from GO and fluorescence recovery. Represented by Ciprofloxacin (CIP), a member of fluoroquinolones, the fluorescence emission increased with the increasing of CIP concentrations from 8 nM to 500 nM, and the detection limit was 0.42 nM. The spiked recoveries in real samples of honey and milk were 91.5-96.9 % and 90.3-95.2 %, respectively, indicating that the aptasensor was reliable. Moreover, the fluorescence responses of multiple members of fluoroquinolones were found to be consistent, denoting that the fluorescence aptasensor can be used to detect the total amount of multiple members of fluoroquinolones. These results showed that the aptasensor can be used as a promising platform for fluoroquinolones detection.

Recognition of chiral propranolol by fluorescent aptamerlight switch based on GO.

In this work, specific aptamers with affinity for S-propranolol were screened by SELEX technology based on the graphene oxide (GO) adsorption platform, and a GO-FAM labeled aptamer-propranolol fluorescent optical switch system was constructed for the recognition of chiral propranolol. It was found that the fluorescence quenching of FAM labeled aptamer could be caused by the adsorption of GO. However, when S-propranolol was introduced, S-propranolol could pull out the aptamer adsorbed by GO, and the fluorescence of the system could be restored. But, R-propranolol could not be realized. Therefore, a simple and sensitive fluorescent optical switch system was established to identify chiral propranolol and perform highly sensitive detection of S-propranolol.

Fluorescent composite based on peptide nanotubes activating coumarin 6 for sensitive detection of new coccine in food samples.

New coccine (NC), as a kind of common colorant, has been frequently used in our daily life. Herein, the fluorescent composite (PNTs@C6) prepared by the hydrophobic non-covalent interaction between peptide nanotubes and coumarin 6 (C6) was designed for the determination of NC. Due to the activation of C6 by peptide nanotubes, the composite exhibits strong green fluorescence emission, which can be selectively quenched by NC through the inner filter effect. Therefore, a new fluorescent method based on the PNTs@C6 composite for NC detection was constructed. Under optimal conditions, the fluorescence quenching of the sensor exhibits a good linear relationship with the concentration of NC in the range of 0.01-10 µM and the limit of detection is 3.6 nM. Furthermore, the strategy shows simplicity, rapid response and high selectivity and has been successfully applied to the detection of NC in food samples.

Immunolabel-First-Expand-Later Expansion Microscopy Approach Using Stable STED Dyes.

Multiple expansion microscopy approaches have been successfully used in the analysis of centrioles, centrosomes, and cilia, helping to reveal the localization of numerous centrosomal and ciliary proteins at nanoscale resolution. In this chapter, we describe the use of two stable STED dyes in combination with expansion microscopy, which allows the robust detection by conventional and STED microscopy of proteins immunolabeled prior to sample expansion. We demonstrate the stability of these dyes during the crosslinking, polymerization, and denaturation steps of an expansion protocol thereby allowing their use in an immunolabel-first-expand-later approach. Our protocol overcomes the frequent technical limitation of poor, unreproducible binding of primary antibodies to proteins after denaturation. We demonstrate the applicability of this approach by analyzing both a centriole appendage protein Cep164 and a ciliary protein ARL13B.

A novel "off-on" ratiometric fluorescent aptasensor for adenosine detection based on FRET between quantum dots and graphene oxide.

A novel "off-on" ratiometric fluorescent aptasensor was established for adenosine detection based on fluorescence resonance energy transfer (FRET) between CdS QDs, DNA QDs as donor and graphene oxide (GO) as acceptor. Amino-riched DNA QDs covalently bonded to the carboxyl group on the edge of the GO, and with the absorption of the TGA-modified CdS QDs with aptamer (CdS QDs-apt) onto the GO surface via the π-π stacking interaction. The fluorescence of both CdS QDs and DNA QDs were efficiently quenched due to FRET (turn off). When adenosine was present, the specific binding of the aptamer to the target preferentially that released the CdS QDs-apt from GO. The process would inhibit the FRET which contribute to the fluorescence of CdS QDs-apt recovery again (turn on), while the fluorescence intensity of DNA QDs only slightly altered and acted as the reference signal. Thus, a novel "off-on" ratiometric fluorescent aptasensor for adenosine detection was constructed accordingly. There was a good linearity relationship between the ratio of the FL intensity (F595 nm/F464 nm) and the concentration of adenosine in the range of 20.00-180.0 nmol/L with a detection limit of 1.3 nmol/L (S/N = 3, n = 9). Importantly, the feasibility of the developed aptasensor for selective detection of adenosine in serum and urine samples with satisfactory results. The recoveries were observed to be 97.04-100.2 %.

Hybridization chain reaction circuit controller: CRISPR/Cas12a conversion amplifier for miRNA-21 sensitive detection.

MicroRNA (miRNA) is crucial to the diagnose of various diseases. However, the accurate detection of miRNA has been challenging due to its short length and low abundance. Here, we designed a hybridization chain reaction (HCR) circuit controller to initiate the CRISPR/Cas12a conversion amplifier (HCR-Cas12a controller) for sensitive detection of miRNA-21 (miR-21). In the HCR, pre-crRNA was encapsulated in a hairpin structure until the miR-21 was present. Afterward, Cas12a fully exerted its RNase activity to self-mature pre-crRNA. Then, the trans-cleavage activity of Cas12a was initiated by activator. This results in the conversion of biological signals to fluorescent signal. During HCR-Cas12a controller, the circuit formed quickly, while the Cas12a system worked in a short time. The miR-21 was ultra-sensitively detected with the wide detection range of 1 fM - 100 nM, and the calculated limit of detection was 75.4 aM. The sensitivity was an order of magnitude lower than the standard method. The formation of HCR at room temperature does not require a thermal cycler. Additionally, Cas12a can work without the need for precise or expensive instruments. Therefore, our proposed method was suitable for low-resource settings, and provided a technical basis for sensitive detection of miRNA in low concentration range.

Fabrication of next-generation multifunctional LBG-s-AgNPs@ g-C3N4 NS hybrid nanostructures for environmental applications.

Toxic industrial wastes and microbial pathogens in water pose a continuous threat to aquatic life as well as alarming situations for humans. Developing advanced materials with an environmentally friendly approach is always preferable for heterogeneous visible light photocatalysis. As a green reducing tool, LBG-s-AgNPs@ g-C3N4 NS hybrid nanostructures were anchored onto graphitic carbon nitride (g-C3N4) using an environmentally friendly approach of anchoring/decorating AgNPs onto g-C3N4. With the help of advanced techniques, the fabricated hybrid nanostructures were characterized. Using a sheet like matrix of g-C3N4, nanosized and well-defined uniform AgNPs displayed good antibacterial activity as well as superior photodegradation of hazardous dyes, including methylene blue (MB) and Rhodamine B (RhB). Based on the disc diffusion method, three pathogenic microorganisms of clinical significance can be identified by showing the magnitude of their susceptibility. As a result, the following antimicrobial potency was obtained: E. coli ≥ M. luteus ≥ S. aureus. In this study, green synthesized (biogenic) AgNPs decorated with g-C3N4 were found to be more potent antimicrobials than traditional AgNPs. Under visible light irradiation, LBG-s-AgNPs@g-C3N4 NS (0.01 M) demonstrated superior photocatalytic performance: ∼100% RhB degradation and ∼99% of MB degradation in 160 min. LBG-s-AgNPs@g-C3N4 NS showed the highest kinetic rate, 3.44 × 10-2 min-1, which is 27.74 times for the control activity in case of MB dye. While in case of RhB dye LBG-s-AgNPs@g-C3N4 NS showed the highest kinetic rate, 2.26 × 10-2 min-1, which is 17.51 times for the control activity. Due to the surface plasmon resonance (SPR) and reduction in recombination of the electrons and holes generated during photocatalysis, anchoring AgNPs to g-C3N4 further enhanced the photocatalytic degradation of dyes. Using this photocatalyst, hazardous dyes can be efficiently and rapidly degraded, allowing it to be applied for wastewater treatment contaminated with dyes. It also showed remarkable antimicrobial activity towards Gram-ve/Gram + ve pathogens.

Bimolecular Fluorescence Complementation (BiFC) in Host-Virus Interactions.

Bimolecular fluorescence complementation (BiFC) is an assay widely used for studying protein-protein interactions and determining the subcellular localization of proteins. This technique involves fusing the proteins of interest to separate structural domains of a fluorescent protein, followed by transient expression in cells. The interaction between the proteins of interest in vivo allows the reconstitution of the fluorescence that can be visualized by fluorescence microscopy. BiFC has been particularly useful in investigating the interactions between viral and host proteins. Here, we describe the steps involved in preparing expression cassettes that allow the expression of proteins of interest fused to nonfluorescent fragments of yellow fluorescent protein (YFP), Agrobacterium transformations, and agroinfiltration of Nicotiana benthamiana leaves to facilitate virus protein-host protein interactions. Finally, high-resolution images can be obtained by analyzing the leaves under a confocal microscope.

Robust iron-doped manganese oxide nanoparticles from facile fabrication to photo-catalytic degradation application of binary dyes mixture.

The manganese oxide (MnO2 and iron-doped manganese oxide (Fe-MnO2) nanoparticles (NPs) with reduced band gap (Eg) were fabricated through the co-precipitation process. They used to degrade Indigo Carmine (IC) and Rhodamine B (RB) binary mixture in an aqueous medium under solar light irradiation. From FT-IR, the twisting modes of the Mn-O bond and the stretching vibrations of the Fe-Mn-O2 bond were confirmed from the peaks observed at 480 cm-1,584 cm-1,675 cm-1, and 900 cm-1, 1150 cm-1, and 1200 cm-1 respectively. The MnO2 has an optical band gap of 3.2 eV, which was decreased to 3 eV in Fe-MnO2. The zero charge (PZC) point was 8 for Fe-MnO2 and 7 for MnO2. The BET surface area for Fe-MnO2 was 398 m2/g, relatively higher than MnO2 particles, having a surface area of 384 m2/g. The average crystallite sizes calculated from Scherer formulae were 37 nm for MnO2 and 31 nm for Fe-MnO2 NPs. SEM confirmed the irregular morphology of the prepared particles. It was analyzed that agglomeration occurs in MnO2 than the Fe-MnO2. The maximum degradation of IC dye was 99%, and that of RB was 98% at the optimum conditions. The data were best fitted to second-order kinetics.