A novel ascorbic acid ratiometric fluorescent sensor based on ZnCdS quantum dots embedded molecularly imprinted polymer and silica-coated CdTeS quantum dots

Bio(sensors) based on molecularly imprinted polymers and silica materials used for food safety and biomedical analysis: Recent trends and future prospects

In recent decades, analytical techniques have increasingly focused on the precise quantification. Achieving this goal has been accomplished with conventional analytical approaches that typically require extensive pretreatment methods, significant reagent usage, and expensive instruments. The need for rapid, simple, and highly selective identification platforms has become increasingly pronounced. Molecularly imprinted polymer (MIP) has emerged as a promising avenue for developing advanced sensors that can potentially surpass the limitations of conventional detection methods. In recent years, the application of MIP-silica materials-based sensors has garnered significant attention owing to their distinctive characteristics. These types of probes hold a distinct advantage in their remarkable stability and durability, all of which provide a suitable sensing platform in severe environments. Moreover, the substrate composed of silica materials offers a vast surface area for binding, thereby facilitating the efficient detection of even minuscule concentrations of targets. As a result, sensors based on MIP-silica materials have the potential to be widely applied in various industries, including medical diagnosis, and food safety. In the present review, we have conducted an in-depth analysis of the latest research developments in the field of MIPs-silica materials based sensors, with a focus on succinctly summarizing and elucidating the most crucial findings. This is the first comprehensive review of integration MIPs with silica materials in electrochemical (EC) and optical probes for biomedical analysis and food safety.

Label-free fluorescence platform based on SiO2-coated CdTeS quantum dots for trace analysis of Ag+ in environmental water

In this study, a core-shell structural nano-composite material, namely CdTeS@SiO2, is synthesized by a simple silanization of Te-doped CdS quantum dots (CdTeS QDs). Through SiO2 capping, CdTeS QDs not only improve the fluorescence performance effectively, but also greatly enhance the anti-interference ability in the environment. Based on its excellent optical properties, a novel fluorescence sensor is constructed for the ultramicro detection of Ag+. The fluorescence of CdTeS@SiO2 is strongly quenched in the presence of Ag+ and shows good linearity in the range of 0.005-5.0 μmol L-1 with a detection limit as low as 1.6 nmol L-1. This is mainly due to its unique quenching mechanism: Ag+ destroys the spherical structure of SiO2 and promotes the formation of non-radiative electron-hole pairs through electron transfer, leading to fluorescence quenching. At the same time, it competes with Cd for Te, S and MPA on the CdTeS surface, forming Ag-Te, Ag-S and Ag-MPA complexes attached to the CdTeS surface leading to wavelength red-shift. The feasibility of the proposed sensor is demonstrated through spiking experiments, which confirmed the potential value of the constructed fluorescence probe for real-world applications in detecting Ag+ in environmental water.

Nanomaterials-based biosensor and their applications: A review

A sensor can be called ideal or perfect if it is enriched with certain characteristics viz., superior detections range, high sensitivity, selectivity, resolution, reproducibility, repeatability, and response time with good flow. Recently, biosensors made of nanoparticles (NPs) have gained very high popularity due to their excellent applications in nearly all the fields of science and technology. The use of NPs in the biosensor is usually done to fill the gap between the converter and the bioreceptor, which is at the nanoscale. Simultaneously the uses of NPs and electrochemical techniques have led to the emergence of biosensors with high sensitivity and decomposition power. This review summarizes the development of biosensors made of NPssuch as noble metal NPs and metal oxide NPs, nanowires (NWs), nanorods (NRs), carbon nanotubes (CNTs), quantum dots (QDs), and dendrimers and their recent advancement in biosensing technology with the expansion of nanotechnology.

Molecular imprinting-based ratiometric fluorescence sensors for environmental and food analysis

Environmental protection and food safety are closely related to the healthy development of human society; there is an urgent need for relevant analytical methods to determine environmental pollutants and harmful substances in food. Molecular imprinting-based ratiometric fluorescence (MI-RFL) sensors, constructed by combining molecular imprinting recognition and ratiometric fluorescence detection, possess remarkable advantages such as high selectivity, anti-interference ability, high sensitivity, non-destruction and convenience, and have attracted increasing interest in the field of analytical determination. Herein, recent advances in MI-RFL sensors for environmental and food analysis are reviewed, aiming at new construction strategies and representative determination applications. Firstly, fluorescence sources and possible sensing principles are briefly outlined. Secondly, new imprinting techniques and dual/ternary-emission fluorescence types that improve sensing performances are highlighted. Thirdly, typical analytical applications of MI-RFL sensors in environmental and food samples are summarized. Lastly, the challenges and perspectives of the MI-RFL sensors are proposed, focusing on improving sensitivity/visualization and extending applications.

Dual-template molecularly surface imprinted polymer on fluorescent metal-organic frameworks functionalized with carbon dots for ascorbic acid and uric acid detection

In this work, dual-template molecularly imprinted polymer surfaces imprinted on blue fluorescent Cr-based MOF (Cr-MOF) functionalized with yellow emissive carbon dots (Y-CDs) were prepared using l-ascorbic acid (AA) and uric acid (UA) as templates for simultaneous selective recognition of AA and UA. The as-prepared nanocomposite probe (Y-CDs/Cr-MOF@MIP) contains two recognition site cavities and emits a dual well-resolved fluorescence spectra when excited at 390 nm; blue emission (λ_em 450 nm) is due to Cr-MOF, and yellow emission (λ_em 560 nm) is due to Y-CDs. The yellow fluorescence emission of Y-CDs was quenched upon the addition of ascorbic acid, while Cr-MOF's emission remained unaffected. In the same way, the blue fluorescence emission of the Cr-MOFs was quenched in the presence of uric acid, while the yellow emission remained constant. Both emissions were quenched in a sample containing both AA and UA. This can be exploited to design a dual-template biosensor to detect UA and AA simultaneously. The Y-CDs/Cr-MOF@MIP sensor displayed a dynamic linear response for AA in the range 25.0 µM - 425.0 µM with a detection limit of 1.30 µM, and for UA in the range 25.0 µM - 425.0 µM with a detection limit of 1.10 µM. The dual-target probe Y-CDs/Cr-MOF@MIP was highly selective and sensitive for the detection of UA and AA in human urine samples due to the selectivity of the two recognition sites.

Molecularly Imprinted Ratiometric Fluorescence Nanosensors

Molecularly imprinted ratiometric fluorescence (MIR-FL) nanosensors feature recognition selectivity, detection sensitivity, application universality, visualization accuracy, and device portability, and have gained popularity. However, the fluorescence intensity, nanostructure, color range, and practical application of the sensor still face severe difficulties to be solved. New strategies combined with various technologies have been developed to construct MIR-FL nanosensors for expanded applications. This Perspective highlights current resarch challenges and future prospects involving constructions and applications of MIR-FL nanosensors including dual-emission and triple-emission modes. The postimprinting mixing/modification strategies, microdevices, and multitarget detection are focused, and technology synergy, sensitivity/reproducibility improvement, application diversity/portability, etc. are proposed.

Facile Synthesis of Molecularly Imprinted Ratiometric Fluorescence Sensor for Ciguatoxin P-CTX-3C Detection in Fish

Ciguatoxin (CTX) detection methods are essential due to the serious hazard that bioaccumulation in fish and transmission along the food chain poses to human health. We report the rapid and simple development of a dual-emitting, molecularly imprinted, ratiometric fluorescence sensor (MIPs@BCDs/RCDs@SiO₂) to detect ciguatoxin P-CTX-3C with high sensitivity and selectivity. The sensor was fabricated via sol–gel polymerization using monensin as the fragmentary dummy template molecule, blue carbon dots (BCDs) as the response signal, and red carbon dots (RCDs) as the reference signal. The fluorescence emission of BCDs was selectively quenched in the presence of P-CTX-3C, leading to a favorable linear correlation between the fluorescence intensity ratio (I₄₄₀/I₆₇₅) and the P-CTX-3C concentration in the range of 0.001–1 ng/mL with a lower detection limit of 3.3 × 10⁻⁴ ng/mL. According to LC-MS measurement results, the proposed sensor can rapidly detect ciguatoxin P-CTX-3C in coral reef fish samples with satisfactory recoveries and standard deviations. This study provides a promising strategy for rapid trace analysis of marine toxins and other macromolecular pollutants in complex matrices.

Ultrasensitive and highly selective "turn-on" fluorescent sensor for the detection and measurement of melatonin in juice samples

Melatonin (MLT), a hormone related to the regulation of brain functions, is directly related to sleep quality and is considered to be a possible adjuvant therapy for patients needing hospitalization for coronavirus disease 2019 pneumonia, and accurate measurement of MLT is crucial. Herein, a new, highly sensitive, and easy operation fluorescent probe was provided based on Zr metal-organic framework encapsulation into the molecularly imprinted polymer (MOF@MIP). By combining unique properties of MIP and fluorescent MOF, selectivity and operation of the applied method were significantly improved. Different characterization methods, such as XRD, FT-IR, and FE-SEM, were used to confirm the synthesis reliability. MOF@MIP was successfully used for the precise identification and ultrasensitive detection for trace amounts of MLT. The detection mechanism for the analytical system is based on the ''turn-on'' fluorescence (FL) signal in 404 nm. The findings proved that it is possible to detect trace amounts of MLT in real samples including grape, cherry, and sour cherry juice. The linear range and the limit of detection (LOD) for trace amounts of MLT were obtained as 1-100 ng/mL and 0.18 ng/mL, respectively.

Ascorbic acid detector based on fluorescent molybdenum disulfide quantum dots

A rapid and facile method is reported for the detection of ascorbic acid using molybdenum disulfide quantum dots (MoS₂ QDs) as a fluorescence sensor. Water-soluble and biocompatible MoS₂ QDs with the maximum fluorescence emission at 506 nm have been successfully synthesized by hydrothermal method and specific detection for ascorbic acid (AA) was constructed to utilize the modulation of metal ion on the fluorescence of MoS₂ QDs and the affinity and specificity between the ligand and the metal ion. The fluorescence of MoS₂ QDs was quenched by the irreversible static quenching of Fe³⁺ through the formation of a MoS₂ QDs/Fe³⁺ complex, while the pre-existence of AA can retain the fluorescence of MoS₂ QDs through the redox reaction between AA and Fe³⁺. Based on this principle, a good linear relationship was obtained in the AA concentration range 1 to 150 μM with a detection limit of 50 nM. The proposed fluorescent sensing strategy was proven to be highly selective, quite simple, and rapid with a requirement of only 5 min at room temperature (RT), which is particularly useful for rapid and easy analysis. Satisfactory results were obtained when applied to AA determination in fruits, beverages, and serum samples as well as AA imaging in living cells, suggesting its great potential in constructing other fluorescence detection and imaging platforms.