Molecularly imprinted thermosensitive probe based on fluorescent advanced glycation end products to detect α-dicarbonyl compounds and inhibit pyrraline formation

A thermal-sensitive molecularly imprinted optosensing probe based on fluorescent advanced glycation end products (AGEs) was prepared by one-pot hydrothermal synthesis. Carbon dots (CDs) derived from fluorescent AGEs were used as the luminous centers, while molecularly imprinted polymers (MIPs) were wrapped outside of the CDs to form specific target recognition sites to highly selectively adsorb the intermediate product of AGEs of 3-deoxyglucosone (3-DG). Thermosensitive N-isopropylacrylamide (NIPAM) was combined with acrylamide (AM) as co-functional monomers, and ethylene glycol dimethacrylate (EGDMA) was chosen as a cross-linker for targeting identification and detection of 3-DG. Under optimal conditions, the fluorescence of MIPs could be gradually quenched with the adsorption of 3-DG on the surface of MIPs in the linear range of 1-160 μg/L, and the detection limit was 0.31 μg/L. The spiked recoveries of MIPs ranged from 82.97 to 109.94% in two milk samples, and the relative standard deviations were all less than 1.8%. In addition, the inhibition rate for non-fluorescent AGEs of pyrraline (PRL) was 23% by adsorbing 3-DG in the simulated milk system of casein and D-glucose, indicating that temperature-responsive MIPs not only could detect the dicarbonyl compound 3-DG quickly and sensitively, but also had an excellent inhibitory effect on AGEs.

Red-to-blue colorimetric probe based on biomass carbon dots for smartphone-integrated optosensing of Cu(II) and L-cysteine

We constructed a smartphone-integrated optosensor with inexpensive, reversible, environmental friendly, and rapid adsorption to detect Cu(II) and L-cysteine (L-Cys). The key part of this study was to prepare a red-to-blue colorimetric probe from herbaceous andrographis paniculata using one-pot polymerization at room temperature. When Cu(II) existed, the red fluorescence on the surface of the core-shell probe was quenched, while the blue fluorescence of the core did not respond, because the colorimetric probe interacted with the Cu(II) on the surface of red CDs. After L-Cys added, it interacted with the Cu(II) to strip it from the surface of red CDs, resulting in the recovery of fluorescence response. Under optimal conditions, the detection limits of this method for Cu(II) and L-Cys were 71 nM and 12 nM, respectively. Further, the red-to-blue colorimetric probe was integrated into smartphone with a software application to convert fluorescent color images into specific red (R), green (G), and blue (B) values. The spiked recovery of Cu(II) and L-Cys in lake water was verified the feasibility of the developed optosensors with a recovery of 98.2-101.6 % and 103.3-121.6 %. This method for detecting Cu(II) and L-Cys can not only recognize metal ions from actual samples, but also effectively protect CDs from quenching and restore fluorescence.

A highly efficient molecularly imprinted fluorescence sensor for assessing whole wheat grains by the rapid and sensitive detection of alkylresorcinols

To differentiate whole wheat foods from refined wheat foods is still challenging grain industry and confusing consumers. Alkylresorcinols (ARs), as biomarkers of whole wheat grains, can serve for assessing the authenticity of whole wheat foods. Herein, a highly efficient fluorescence sensing platform (CDs@MIP) for rapid and sensitive analysis of ARs was explored, using carbon dots (CDs) as fluorophores and 5-heneicosylresorcinol (C21:0 AR) as template molecules embedded in a molecularly imprinted polymer (MIP) coating. Benefiting from the specific cavities in the probe and a photo-induced electron transfer effect, the fluorescence intensity of CDs@MIP was significantly quenched in the presence of C21:0 AR, exhibiting a superior binding efficiency and selectivity. As a result, the fabricated optical sensor delivered a wide linear range of C21:0 AR from 0.015 to 60 μg mL-1 with an ultralow detection limit of 4 ng mL-1. It was noteworthy that the sensor was successfully applied for the rapid detection of C21:0 AR in commercial whole-wheat foods as well as visualization analysis on the test paper, comprehensively validating the practicality and efficacy of CDs@MIP based fluorescence assay. The study provides a rapid and sensitive detection method of C21:0 AR, paving a new way for guiding grain industry to effectively qualify the authenticity and to quantify the content of whole wheat in wheat-based foods.

Red emissive N-doped carbon dots encapsulated within molecularly imprinted polymers for optosensing of pyrraline in fatty foods

A novel and facile method was proposed for preparation of red emissive N-doped carbon dots encapsulated within molecularly imprinted polymers (RNCDs@MIPs) using a one-pot room-temperature reverse microemulsion polymerization. RNCDs used citric acid and urea as carbon and nitrogen sources by one-step solvothermal synthesis with the optimum emission of 620 nm. Unique optical properties of RNCDs coupled with high selective MIPs make the RNCDs@MIPs conjugate capable to adsorb specific targets of pyrraline (PRL), such a binding event was then transduced to quench fluorescence response signal of the RNCDs. RNCDs@MIPs for PRL showed linearity from 0.1 to 40 μg/L, with a detection limit of 65 ng/L. The RNCDs@MIPs exhibited a good reproducibility of 4.67% obtained from four times of rebinding for PRL. The optosensing probe was successfully applied to the detection of PRL in fatty foods with the spiked recovery of 85.93-106.96%.

Molecularly imprinted bulk and solgel optosensing based on biomass carbon dots derived from watermelon peel for detection of ethyl carbamate in alcoholic beverages

Biomass carbon dots synthesized by biological waste conform to the trend of ecological environmental protection and the requirements of green chemistry, which show great application potential in practice. In the study, we used watermelon peels as the raw materials to synthesize a novel blue biomass carbon dots (CDs) by a hydrothermal process with high fluorescence quantum yield of 22.8%. Through bulk polymerization and solgel method, two kinds of core-shell nanospheres were developed as fluorescent probes to recognize and detect ethyl carbamate (EC) rapidly without complex samples pretreatment. The obtained CDs@MIPs integrated the high-performance optical characteristics of CDs with excellent selectivity and adsorption of MIPs, which showed ideal linear relationships in the EC concentration range 1-120 μg L^-1 and low LOD of 0.57 μg L^-1 and 0.94 μg L^-1, respectively. Both CDs@MIPs have a short equilibration time which was around 20 min, and the imprinting factors (IF) are 4.04 and 2.62. The recoveries of the six spiked samples were satisfying, and the RSD precisions were lower than 5.57%. Gas chromatography-mass spectrometry was seen as a parallel analysis to validate the correctness of the results, which indicated the practicability and reliability of the developed method. This proposal strategy of optical sensors provided an effective channel for trace EC recognition, with numerous advantages, involving eco-friendly, low cost, high sensitivity, separation effect, and good selectivity.

Chiroptical-responsive nanoprobe for the optosensing of chiral amino acids

A supersensitive chiroptical-responsive system of enantioselectively recognizing L- and D-tryptophan (Trp) based on ( +)-diacetyl-L-tartaric anhydride-functionalized 1,3,5-triformylphloroglucinol (DTA-functionalized Tp) was constructed for the first time. With a high fluorescence quantum yield of 15.2% and fluorescence lifetime of 57.6 μs, DTA-functionalized Tp as both fluorescent and chiral recognition nanoprobe was used for the discrimination of L- and D-Trp with excitation/emission maxima at 330/490 nm within 3 min. The linear range of the fluorescence sensing was 0.002-0.15 μg mL^-1, and the detection limit achieved 1.4 ng mL^-1. Furthermore, a smartphone was employed as a detector and processor to couple with the chiroptical-responsive nanoprobe for establishing a novel and visual integration system for rapid and real-time detection of chiral amino acids with a detection limit of 13 ng mL^-1. The spiked recoveries of L-Trp in two commercially available functional beverages ranged from 86.00 to 118.33% in fluorescence and smartphone-based sensing system. Based on the excellent chiroptical-responsive effects, high stability, and biocompatibility, the chiroptical-responsive nanoprobe was successfully applied to visual optosensing and fluorescence imaging in response to L- and D-Trp in HeLa cells. This discrimination methodology with high sensitivity and enantioselectively shows great potential for in-site visually monitoring chiral amino acids in real food samples and tracking physiological processes.

A smartphone-integrated optosensing platform based on red-emission carbon dots for real-time detection of pyrethroids

This report described the development of an optosensing platform based on red-emission carbon dots (RCDs) integrated with a smartphone application that, together, can detect pyrethroids in real time. Based on the high stability and selectivity of molecular imprinting technology, RCDs-based optosensing imprinted polymers was obtained by using a one-pot inverse microemulsion surface imprinting method. Lambda-cyhalothrin (LC), which is a pyrethroid pesticide, can interact with the widely distributed -NH₂ groups on the surface of the RCD-based optosensing nanomaterials to achieve fixed-point adsorption. The quantitative detection of pyrethroids in a wide concentration range (1-120 μg/L) could be achieved, and the limit of detection (LOD) was 0.89 μg/L. Furthermore, a portable UV light box combined with a smartphone was used to convert the change in fluorescence of the RCDs-based optosensing nanomaterials into specific values upon adding pyrethroids, and the LOD by using smartphone was 6.66 μg/L. The developed platform has numerous advantages, including low cost, simple operation, high sensitivity, and good specificity, among others, and it achieves on-site visualization and rapid detection.