Dual amplification in a fluorometric acetamiprid assay by using an aptamer, G-quadruplex/hemin DNAzyme, and graphene quantum dots functionalized with D-penicillamine and histidine

Topological effect of an intramolecular split G-quadruplex on thioflavin T binding and fluorescence light-up

In this work, the topological effect on binding interaction between a G-quadruplex and thioflavin T (ThT) ligand was systematically investigated on a platform of an intramolecular split G-quadruplex (Intra-SG). Distinct fluorescence changes from ThT were presented in the presence of distinct split modes of Intra-SG structures and an intriguing phenomenon of target-induced fluorescence light-up occurred for split modes 2 : 10, 5 : 7 and 8 : 4. It was validated that hybridization between the Intra-SG spacer and target did not unfold the G-quadruplex, but facilitated the ThT binding. Moreover, the 3' guanine-rich fragment of Intra-SG was very susceptible to topology variation produced by the bound target strand. Additionally, a bioanalytical method was developed for ultrasensitive gene detection, confirming the utility of the ThT/Intra-SG complex as a universal signal transducer. It is believed that the results and disclosed rules will inspire researchers to develop many new DNA-based signal transducers in the future.

Developments in food neonicotinoids detection: novel recognition strategies, advanced chemical sensing techniques, and recent applications

Neonicotinoid insecticides (NEOs) are a new class of neurotoxic pesticides primarily used for pest control on fruits and vegetables, cereals, and other crops after organophosphorus pesticides (OPPs), carbamate pesticides (CBPs), and pyrethroid pesticides. However, chronic abuse and illegal use have led to the contamination of food and water sources as well as damage to ecological and environmental systems. Long-term exposure to NEOs may pose potential risks to animals (especially bees) and even human health. Consequently, it is necessary to develop effective, robust, and rapid methods for NEOs detection. Specific recognition-based chemical sensing has been regarded as one of the most promising detection tools for NEOs due to their excellent selectivity, sensitivity, and robust interference resistance. In this review, we introduce the novel recognition strategies-enabled chemical sensing in food neonicotinoids detection in the past years (2017-2023). The properties and advantages of molecular imprinting recognition (MIR), host-guest recognition (HGR), electron-catalyzed recognition (ECR), immune recognition (IR), aptamer recognition (AR), and enzyme inhibition recognition (EIR) in the development of NEOs sensing platforms are discussed in detail. Recent applications of chemical sensing platforms in various food products, including fruits and vegetables, cereals, teas, honey, aquatic products, and others are highlighted. In addition, the future trends of applying chemical sensing with specific recognition strategies for NEOs analysis are discussed.

Dual DNAzyme-catalytic assembly of G-quadruplexes for inducing the aggregation of gold nanoparticles and developing a novel antibiotic assay method

By utilizing a target biorecognition reaction to induce the self-assembly of G-quadruplexes and the aggregation of gold nanoparticles (Au NPs), this work develops a novel colorimetric biosensing method for kanamycin (Kana) antibiotic detection. The compact G-quadruplex structure was assembled from its two half-split sequences which were designed in two hairpin substrates of the Mg²⁺-dependent DNAzyme (MNAzyme). Besides hybridizing with the aptamer strand, the MNAzyme sequence was also split into two half fragments to be designed in the two substrates. Upon the aptamer-recognition reaction toward Kana, the MNAzyme strand could be quantitatively released to cause the exposure of the split G-quadruplex-sequences on two hairpin substrate-modified Au NPs and simultaneous release of two half fragments of the MNAzyme-sequence. Thus, the K⁺-assisted self-folding of G-quadruplexes causes the cross-linking of the two Au NPs to realize the Au NP aggregation-based colorimetric signal output (measured at the largest absorption peak near 520 nm). Meanwhile, the self-assembled formation of the second MNAzyme drastically amplified the signal response. Under the optimal conditions, a wide linear range from 0.1 pg mL^-1 to 10 ng mL^-1 and an ultrahigh sensitivity with the detection limit of 76 fg mL^-1 were obtained. The dose-recovery experiments in real samples showed satisfactory results with recoveries from 98.4 to 105.4% and relative errors compared with the ELISA method less than 4.1%. Due to the high selectivity, excellent repeatability and stability, and simple manipulation, this method indicates a promising potential for practical applications. A novel homogeneous biosensing method was developed for the convenient detection of the kanamycin antibiotic. The target biorecognition-induced and dual DNAzyme-catalytic assembly of G-quadruplexes enabled the amplified aggregation of gold nanoparticles for the simple, cheap, stable, and ultrasensitive colorimetric signal transduction of the method.

A biosensor based on interchain reactions for the detection of acetamipirid and the construction of basics logic gates OR and AND

An enzyme-free and label-free fluorescent DNA aptasensor was constructed with computer assistance based on thermodynamic deviation driving interchain reactions. In this work, in the presence of target acetamiprid, the released trigger strand C-apt could open hairpin Hp1, which in turn triggered the strand displacement reaction and catalyzed the self-assembly of hairpins Hp1 and Hp2, so that the guanine base rich stem in Hp2 was opened. In the presence of K+ and NMM, the G-rich moiety could form a G-quadruplex and emit strong fluorescence at a specific excitation wavelength. The proposed strategy enables sensitive detection of acetamiprid at concentrations as low as 54.3 pM. Most importantly, computer-assisted analysis of the thermodynamic properties of nucleic acid strands and simulation of the reaction process and conditions of the proposed model before conducting biological experiments theoretically proves this strategy feasible and may simplify subsequent biological experiments. In addition, basic molecular logic gates, including OR and AND, were constructed based on this detection principle, and simulation tests and biological experiments were performed. The final results show that this strategy can not only have some applications in the field of food safety and environmental monitoring, but also provide a certain way for the development of molecular logic computing.

Developing a three-input cascade DNA logic gate based on the biological characteristics of metal ion-GO, combined with analysis and verification

Due to the limitation of technology, electronic computing is approaching the limit of technology, and new computing tools need to be developed. Here, we build a three-input cascade logic gate based on the advantages of biomolecules, particularly DNA, in the construction of computational logic systems, combined with metal ions and graphene oxide (GO). It is worth mentioning that this study uses a variety of research methods. In addition to the commonly used biological experiments, NUPACK and visual DSD simulation methods are used for analysis, and orthogonal, standardized and other statistical means are used to simplify the experimental process and make the results intuitive. Finally, the designed three-input logic gate is successfully constructed, and it is found that it may have the potential to realize complex computing.

Do amino acid functionalization stratagems on carbonaceous quantum dots imply multiple applications? A comprehensive review

Amino acids are the noteworthy entity among biological molecules with diverse properties such as zwitterionic and amphoteric. Functionalizing carbon-based quantum dots using amino acids might be used for the extreme enhancement of electronic and optical properties of quantum dots and improve the performance of the resultant amino acid-functionalized quantum dots. The amino acid-functionalized quantum dots are highly soluble, sustainable, and biocompatible with virtuous optical and electrical performance, which makes them potential and suitable candidates for fabricating optoelectronic devices. The tenacity of using amino acids as functional groups to functionalize quantum dots and their novel properties are conferred to attain their multiple applications. The goal of this review is to provide the choices of amino acids based on the desired applications and a variety of functionalization techniques to make them a noteworthy material for future applications. The method of one-step and two-step functionalization strategies along with the properties of the resultant functionalized quantum dots and their plausible applications and future scope of the material are highlighted. Amidation is the basic principle behind the functionalization of quantum dots with amino acids. This review would be an exciting prospect to explore the pathways of the possible applications in different domains, in which the amino acid-functionalized quantum dots have not yet been explored. Further, this review article helps in pitching a variety of prominent applications right from sensors to energy storage systems either using the optical property or electronic property of amino acid-functionalized quantum dots.

Recent progress on graphene quantum dots-based fluorescence sensors for food safety and quality assessment applications

The versatile photophysicalproperties, high surface-to-volume ratio, superior photostability, higher biocompatibility, and availability of active sites make graphene quantum dots (GQDs) an ideal candidate for applications in sensing, bioimaging, photocatalysis, energy storage, and flexible electronics. GQDs-based sensors involve luminescence sensors, electrochemical sensors, optical biosensors, electrochemical biosensors, and photoelectrochemical biosensors. Although plenty of sensing strategies have been developed using GQDs for biosensing and environmental applications, the use of GQDs-based fluorescence techniques remains unexplored or underutilized in the field of food science and technology. To the best of our knowledge, comprehensive review of the GQDs-based fluorescence sensing applications concerning food quality analysis has not yet been done. This review article focuses on the recent progress on the synthesis strategies, electronic properties, and fluorescence mechanisms of GQDs. The various GQDs-based fluorescence detection strategies involving Förster resonance energy transfer- or inner filter effect-driven fluorescence turn-on and turn-off response mechanisms toward trace-level detection of toxic metal ions, toxic adulterants, and banned chemical substances in foodstuffs are summarized. The challenges associated with the pretreatment steps of complex food matrices and prospects and challenges associated with the GQDs-based fluorescent probes are discussed. This review could serve as a precedent for further advancement in interdisciplinary research involving the development of versatile GQDs-based fluorescent probes toward food science and technology applications.

Sensitive recognition of ractopamine using GQDs-DPA as organic fluorescent probe

A novel spectrofluorimetric sensing platform was designed for Ractopamine measurement in aqueous and plasma samples. d-penicillamine functionalized graphene quantum dots (DPA-GQDs) was utilized as a fluorescence probe, which was synthesized through the pyrolysis of citric acid in the presence of DPA. This one-pot down-top strategy causes to high-yield controllable synthesis method. The reaction time and probe concentration were optimized. Then, the fluorescence intensity of aqueous samples containing different Ractopamine concentrations and 500 ppm DPA-GQDs were measured at 25°C with an excitation wavelength of 274 nm. The sensing platform was also applied to detect Ractopamine in untreated plasma samples. The fluorescence spectroscopy technique responses indicated a linear relationship between the peak fluorescence intensity and ractopamine concentration in the range of 0.25-15 ppm with low limit of quantification of 0.25 ppm was for aqueous and plasma samples, respectively.

Determination of acetamiprid using electrochemiluminescent aptasensor modified by MoS2QDs-PATP/PTCA and NH2-UiO-66

A novel aptasensor has been fabricated based on the resonance energy transform (RET) system from MoS₂QDs-PATP/PTCA (donor) to NH₂-UiO-66 (acceptor). The electrochemiluminescence (ECL) signal of PTCA was greatly amplified due to the decoration of MoS₂QDs-PATP, and the NH₂-UiO-66 was utilized to label the signal probe DNA (pDNA), which hybridizes with the exposed aptamer anchored on the surface of MoS₂QDs-PATP/PTCA. With the target acetamiprid, the specific binding of acetamiprid to aptamer causes the connection between the donor and the acceptor to be interrupted and produce an "on" ECL signal. Thus, an "off-on" ECL sensing platform for sensitive and selective acetamiprid assay was designed. Under the optimal condition, the ECL signal of the aptasensor was found to be linearly related to the logarithm of the acetamiprid concentration ranging from 0.1 fM to 0.1 μM with a detection limit of 0.064 fM. More importantly, the recovery rate of the ECL aptasensor was calculated to be 98.7 ~ 106% with a RSD lower 5.1% for the residual acetamiprid assay in real food samples, which indicated that the aptasensor has high potential for practical applications.

Boron-doped and serine and histidine-functionalized graphene quantum dots with strong yellow fluorescence emissions for highly sensitive detection of carbofuran in cucumber and cabbage

The weak fluorescence of graphene quantum dots upon visible-light excitation limits their applications.

A smartphone-based platform for point-of-use determination of alkaline phosphatase as an indicator of water eutrophication

A smartphone-based detection platform for the determination of alkaline phosphatase (ALP) is described. The method is based on the rational design of the stimulus-response of 7-methoxycoumarin-3-carboxylic acid (7-MC-3-COOH)-functionalized Eu-AMP infinite coordination polymer (ICP) nanoparticles. The blue fluorescence of 7-MC-3-COOH at 403 nm was suppressed, while the red fluorescence of Eu³⁺ at 615 nm was sensitized after the formation of 7-MC-3-COOH@Eu-AMP ICP. Upon exposure to ALP, the dephosphorylation of AMP resulted in the destruction of 7-MC-3-COOH@Eu-AMP ICP, and thereby, the blue fluorescence of 7-MC-3-COOH recovered; in the meantime, the sensitized red fluorescence was quenched. With the fluorescence intensity ratio F₆₁₅/F₄₃₀ as the signal readout, ALP can be detected within a concentration range 0.001 to 0.15 U mL^-1, and the limit of detection (LOD) was 0.00035 U mL^-1. Moreover, fluorescence color changes from red to blue could also be recognized by a portable device with the smartphone as a signal reader, and direct point-of-use testing (POUT) for ALP within a concentration range 0.005 to 0.7 U mL^-1 could be realized, with LOD of 0.0015 U mL^-1. Endowed with high sensitivity and superior reliability, the assay enabled direct monitoring of P-related water eutrophication in a freshwater lake with ALP as an indicator. Graphical abstract A smartphone-based platform for point-of-use determination of alkaline phosphatase.