Selective optosensing of clenbuterol and melamine using molecularly imprinted polymer-capped CdTe quantum dots

Hydrogel-based fluorescence assay kit for simultaneous determination of ceftazidime and avibactam

Monitoring the concentration of antibiotics rapidly and cost-effectively is crucial for accurate clinical medication and timely identification of drug-induced illnesses. Here, we constructed a novel fluorescent assay kit to monitor Zavicefta, an effective antibiotic composed of avibactam (AVI) and ceftazidime (CFZ) to treat carbapenem-resistant gram-negative bacteria infections. AVI can emit fluorescence, but CFZ cannot. To enable simultaneous measurement of both in one kit, we designed molecularly imprinted polymer (MIP) modified quantum dots (QDs) for CFZ determination. MIPs have received significant attention as an artificial antibody due to their exceptional specificity for various targets, particularly drugs with small molecular weight. Under the excitation wavelength of 350 nm, the detection process involves a decrease in QDs' fluorescence signal at 600 nm owing to the "gate effect" between MIP and CFZ and the internal filtration effect between CFZ and QDs. Simultaneously, a fluorescence emission characteristic peak at 420 nm for AVI emerges. In addition, to simplify the operation procedure and improve determination throughput, the detection agents were incorporated into a hydrogel and placed in a 96-well plate, enabling concurrent quantification of AVI and CFZ within the respective range of 80-1000 μM and 1-1000 μM. The developed assay kit successfully determined AVI and CFZ in human serums and therapeutic drug monitoring in a live rabbit model. Recoveries of AVI and CFZ were 92.7-114%, with relative standard deviations below 6.0%. Moreover, a smartphone was employed to read the fluorescence signals, which was beneficial for cost reduction and out-of-lab analysis. This study will deliver a pragmatic resolution to developing high-throughput assay kits for drug determination.

Molecularly Imprinted Polymer-Coated CdTe Quantum Dots for Fluorometric Detection of Sulfonamide Antibiotics in Food Samples

This work reports the development and application of a highly selective core@shell-based quantum dot-molecularly imprinted polymer (QD@MIP) sensor for the detection of sulfadiazine (SDZ)-an antibiotic which belongs to the sulfonamide family. The synthesis of the smart material or MIP (molecularly imprinted polymer) was carried out by a precipitation method directly on the quantum dot surface, which played the role of a fluorescent probe in the optical sensor. The synthesized polymer was characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. Fluorescence experiments were performed in order to evaluate the effects of pH, interaction time of the QD@MIP with the analyte and SDZ concentration in different matrices. Under optimized conditions, a linear concentration range of 10.0-60.0 ppm and a limit of detection of 3.33 ppm were obtained. The repeatability and reproducibility of the proposed QD@MIP were evaluated in terms of the RSD, where RSD values of less than 5% were obtained in both tests. Selectivity studies were carried out in the presence of four possible interfering substances with quenching properties, and the signals obtained for these interferents confirmed the excellent selectivity of the proposed sensor; the imprinting factor value obtained for SDZ was 1.64. Finally, the proposed sensor was applied in real animal-based food samples using a spiked concentration of SDZ, where the recovery values obtained were above 90% (experiments were performed in triplicate).

Monitoring leaching of Cd2+ from cadmium-based quantum dots by an Cd aptamer fluorescence sensor

Quantum Dots (QDs) have been demonstrated with outstanding optical properties and thus been widely used in many biological and biomedical studies. However, previous studies have shown that QDs can cause cell toxicity, mainly attributable to the leached Cd2+. Therefore, identifying the leaching kinetics is very important to understand QD biosafety and cytotoxicity. Toward this goal, instrumental analyses such as inductively coupled plasma mass spectrometry (ICP-MS) have been used, which are time-consuming, costly and do not provide real-time or spatial information. To overcome these limitations, we report herein a fast and cost-effective fluorescence sensor based a Cd2+-specific aptamer for real-time monitoring the rapid leaching kinetics of QDs in vitro and in living cells. The sensor shows high specificity towards Cd2+ and is able to measure the Cd2+ leached either from water-dispersed CdTe QDs or two-layered CdSe/CdS QDs. The sensor is then used to study the stability of these two types of QDs under conditions to mimic cellular pH and temperature and the results from the sensor are similar to those obtained from ICP-MS. Finally, the sensor is able to monitor the leaching of Cd2+ from QDs in HeLa cells. The fluorescence aptamer sensor described in this study may find many applications as a tool for understanding biosafety of numerous other Cd-based QDs, including leaching kinetics and toxicity mechanisms in living systems.

Boronate affinity-based template-immobilization surface imprinted quantum dots as fluorescent nanosensors for selective and sensitive detection of myricetin

In order to prepare a kind of efficient fluorescence sensors for determination of cis-diol-containing flavonoids, novel imprinted quantum dots for myricetin (Myr) were prepared based on boronate affinity-based template-immobilization surface imprinting. The obtained boronate affinity-based surface imprinted silica (imprinted APBA-functionalized CdTe QDs) was used as recognition elements. The quantum dots were used as signal-transduction materials. Under the optimum conditions, according to fluorescence quenching of imprinted APBA-functionalized CdTe QDs by Myr, the imprinting factor (IF) for Myr was evaluated to be 7.88. The result indicated that the boronate affinity functionalized quantum dots coated with imprinted silica were successfully prepared. The prepared imprinted APBA-functionalized CdTe QDs exhibited good sensitivity and selectivity for Myr. The fluorescence intensity was inversely proportional to the concentration of Myr in the 0.30-40 μM concentration range. And its detection limit was obtained to be 0.08 μM. Using the fluorescence sensors, the detection of Myr in real samples was successfully carried out, and the concentration of Myr in green tea and apple juice samples was evaluated to be 2.26 mg/g and 0.73 mg/g, respectively. The recoveries for the spiked green tea and apple juice samples were 95.2-105.0% and 91.5-111.0%, respectively. This study also provides an efficient fluorescent detection method for cis-diol-containing flavonoids in real samples.

The creation of selective imprinted cavities on quartz crystal microbalance electrode for the detection of melamine in milk sample

Molecularly imprinted polymer based nanofilms specific to melamine were synthesized on quartz crystal microbalance (QCM) electrode surface. Contact angle measurements, atomic force microscopy, ellipsometry and scanning electron microscopy were used for characterizations process. Some of the findings of the study are as follows: pH 6.0 was found as optimal working pH for melamine detection. Prepared MIP QCM electrode showed a linearity of 99.53% in the concentration range of 50-1000 ng/mL. Langmuir-Freundlich hybrid model was the best fitted isotherm for whole concentration range. The performance of MIP QCM electrode was also confirmed by determining of melamine in melamine spiked milk samples. As a conclusion, the results figured out that not only QCM nanosensor for specific melamine detection but also polymerization strategy were classified as an intriguing alternative for developing new melamine sensing platforms. Limit of detection (LOD) and limit of quantification (LOQ) were calculated as 2.3 ng/mL and 7.8 ng/mL, respectively.

A label-free aptasensor for clenbuterol detection based on fluorescence resonance energy transfer between graphene oxide and rhodamine B

A label-free aptasensor for clenbuterol was developed through the fluorescence resonance energy transfer mechanism by using an aptamer as the recognition element, rhodamine B as the fluorescence probe and graphene oxide as the fluorescence quencher.

Nanohybrid magnetic composite optosensing probes for the enrichment and ultra-trace detection of mafenide and sulfisoxazole

Nanohybrid magnetic optosensing probes were designed and fabricated to enrich and detect ultra-trace levels of mafenide and sulfisoxazole simultaneously. The probes combined the high affinity of MIL-101 and the sensitivity of graphene quantum dots (GQDs) and cadmium telluride quantum dots (CdTe QDs) with the selectivity and rapid separation provided by a magnetic molecularly imprinted polymer (MMIP). Since the MIL101-MMIP-GQD and MIL101-MMIP-CdTe QD probes produced high fluorescence emission intensities at 435 and 572 nm, respectively, mafenide and sulfisoxazole could be simultaneously detected. Quantitative analysis was based on fluorescence quenching produced by binding between target molecules and imprinted recognition cavities. In the optimal experimental condition, emission intensity was quenched linearly with increasing analyte concentration from 0.10 to 25.0 μg L^-1. Limit of detection was 0.10 μg L^-1 for mafenide and sulfisoxazole. The developed optosensor was applied to detect ultra-trace amounts of mafenide and sulfisoxazole in bovine milk. Recoveries of mafenide and sulfisoxazole in spiked bovine milk ranged from 80.4 to 97.9% with RSDs <5% and the analysis results agreed well with HPLC analysis. The proposed probes provided excellent sensitivity, selectivity, ease and convenience of use.

A review of the incorporation of QDs and imprinting technology in optical sensors – imprinting methods and sensing responses

This review aims to cover the simultaneous method of using molecularly imprinted technology and quantum dots (QDs) as well as its application in the field of optical sensors.

A new potentiometric platform: Antibody cross-linked graphene oxide potentiometric immunosensor for clenbuterol determination

An immunosensor is based on the signal measurement obtained upon the reaction of an antibody antigen complex. It plays a significant role in various fields such as environmental analysis, production monitoring, drug detection or screening, veterinary medicine, and animal food. In this study, an antibody crosslinked graphen oxide (GO)-based potentiometric sensor has been developed for fast, simple, and economical detection of clenbuterol. In this context, the photosensitive amino acid bound GO platform is synthesized and used for the preparation of electrode material. Then, polymeric structure is characterized by infrared spectroscopy, and the performance of immunonano platform prepared by potentiometric sensor is evaluated. The effect of pH, response time, selectivity, and sensitivity is investigated. Under the optimized conditions, a simple and rapid method for the determination of clenbuterol from milk sample is established by immuno-potentiometric sensor. The detection limit has found to be 0.87 × 10^-9 mmol L^-1 for this immuno-potentiometric sensor. This immuno-potentiometric sensor has optimum pH at 7.0, a wide linear response (1.0 × 10^-2 to 1.0 × 10^-9 mmol L^-1 ), rapid response time (2 Min) and 36 weeks operational lifetime.

Highly sensitive and selective detection of 4-nitroaniline in water by a novel fluorescent sensor based on molecularly imprinted poly(ionic liquid)

A novel molecularly imprinted fluorescent sensor for the determination of 4-nitroaniline (4-NA) was synthesized via free radical polymerization with 3-[(7-methoxy-2-oxo-2H-chromen-4-yl)methyl]-1-vinyl-1H-imidazol-3-ium bromide as the fluorescence functional monomer, 4-NA as the template molecule, ethylene glycol dimethacrylate as the cross-linker, and 2,2'-azo(bisisobutyronitrile) as the initiator. The obtained fluorescent poly(ionic liquid) was characterized through Fourier transform infrared, scanning electron microscopy, Brunauer-Emmett-Teller analysis, and fluorescence spectrophotometry. The fluorescent sensor had high fluorescence intensity, short detection time (0.5 min), good selectivity, and excellent sensitivity (limit of detection = 0.8 nM) for 4-NA, with good linear relationships of 2.67-10,000 nM. The practical applicability of the fluorescence sensor in detecting 4-NA in industrial wastewater and spiked environmental water was demonstrated, and a satisfactory result was obtained. Graphical abstract Highly sensitive and selective detection of 4-nitroaniline in water by a novel fluorescent sensor based on molecularly imprinted poly(ionic liquid).

Fluorescent nanomaterials combined with molecular imprinting polymer: synthesis, analytical applications, and challenges

Fluorescent nanomaterials (FNMs) and molecular imprinted polymers (MIPs) have been widely used in analytical chemistry for determination. However, low selectivity of FNMs and low sensitivity of MIPs hinder their applications. Combining the merits of FNMs and MIPs, FNMs coated with MIPs (FNMs@MIPs) were proposed to solve those problems. Carbon dots, semiconductor quantum dots, noble metal nanoparticles, silica nanoparticles, and covalent-organic frameworks have been reported to be coated with MIPs. In order to overcome challenges for FNMs@MIPs, such as the lack of handy synthesis routes, incompatibility with aqueous solutions, heterogeneous size of particles, leakage of template molecules, the biocompatibility of FNMs@MIPs, and the inference between FNMs and MIPs, scientists proposed some solutions in recent years. We comprehensively review the newest advances of the FNMs@MIPs, and predict the direction of the future development. Graphical abstract.

A fluorescence microplate assay based on molecularly imprinted silica coated quantum dot optosensing materials for the separation and detection of okadaic acid in shellfish

Molecularly imprinted polymers (MIPs) are attracting substantial interest as artificial plastic antibodies because of their biometric capability for targeting small molecules. In this study, molecularly imprinted silica material-coated quantum dots (MIS-QDs) with selective recognition capability to okadaic acid (OA) were developed and characterized. The synthesized MIS-QDs with specific imprinting cavities exhibited excellent recognition capability similar to those of biological antibodies and high fluorescence (FL) quenching selectivity for OA. Furthermore, the MIS-QDs with unsaturated bonds were immobilized onto the surface of 96-well microplates by cold plasma-induced grafting. A novel direct competitive microplate assay strategy was then proposed. The FL quenching properties of the developed microplate assay showed an excellent linear relationship with OA in the range of 10.0-100.0 μg/kg with a correlation coefficient of 0.9961. The limit of detection for OA was 0.25 μg/kg in the shellfish samples. The mean quantitative recoveries were 92.5%-101.0% and 92.9%-101.3%, with relative standard deviations of <7.7% and 7.6% for pure solvents and purified shellfish samples, respectively. The established microplate assay strategy can be used as a rapid and high-throughput method for analyzing OA marine toxins in biological samples.

Study of Physico-Chemical Changes of CdTe QDs after Their Exposure to Environmental Conditions

The irradiance of ultraviolet (UV) radiation is a physical parameter that significantly influences biological molecules by affecting their molecular structure. The influence of UV radiation on nanoparticles has not been investigated much. In this work, the ability of cadmium telluride quantum dots (CdTe QDs) to respond to natural UV radiation was examined. The average size of the yellow QDs was 4 nm, and the sizes of green, red and orange QDs were 2 nm. Quantum yield of green CdTe QDs-MSA (mercaptosuccinic acid)-A, yellow CdTe QDs-MSA-B, orange CdTe QDs-MSA-C and red CdTe QDs-MSA-D were 23.0%, 16.0%, 18.0% and 7.0%, respectively. Green, yellow, orange and red CdTe QDs were replaced every day and exposed to daily UV radiation for 12 h for seven consecutive days in summer with UV index signal integration ranging from 1894 to 2970. The rising dose of UV radiation led to the release of cadmium ions and the change in the size of individual QDs. The shifts were evident in absorption signals (shifts of the absorbance maxima of individual CdTe QDs-MSA were in the range of 6–79 nm), sulfhydryl (SH)-group signals (after UV exposure, the largest changes in the differential signal of the SH groups were observed in the orange, green, and yellow QDs, while in red QDs, there were almost no changes), fluorescence, and electrochemical signals. Yellow, orange and green QDs showed a stronger response to UV radiation than red ones.

Selective and sensitive determination of celastrol in traditional Chinese medicine based on molecularly imprinted polymers modified Mn-doped ZnS quantum dots optosensing materials

In this work, we proposed a facile strategy to prepare molecularly imprinted polymers (MIPs) modified Mn-doped ZnS quantum dots (QDs) as optosensing materials via sol-gel polymerization for specific recognition of celastrol (Cel) in traditional Chinese medicine (TCM). Firstly, L-Cysteine (L-Cys) modified Mn-doped ZnS QDs (L-Cys@Mn-ZnS) was used as imprinting substrate. The amino and carboxyl groups on the surface of Mn-ZnS QDs can provide more binding sites for imprinting polymerization. Then, the fluorescent MIPs was synthesized in the presence of L-Cys@Mn-ZnS QDs, template celastrol, 3-aminopropyl triethoxysilane (APTES) and ammonium hydroxide in the ethanol-water (9/1, v/v) solution. The morphology and structure of the products were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffractometer (XRD) and X-ray photoelectron spectroscopy (XPS). The resulting MIPs functionalized Mn-doped ZnS QDs (denoted as MIPs@L-Cys@Mn-ZnS QDs) had higher imprinting factor of 14.19 and significant selectivity. The MIPs@L-Cys@Mn-ZnS QDs as fluorescent probe exhibited sensitive response to Cel in the linear range from 0.1 μM to 3.5 μM and the limit of detection was estimated to be 35.2 nM. The probe was also applied for the detection of Cel in traditional Chinese medicine with recovery ranged from 88.0%-105.0%. The results confirmed that MIPs@L-Cys@Mn-ZnS QDs could efficiently and specifically capture Cel from actual complex traditional Chinese medicine samples.

Determination of cis-diol-containing flavonoids in real samples using boronate affinity quantum dots coated with imprinted silica based on controllable oriented surface imprinting approach

Novel boronate affinity imprinted quantum dots (BA-CdTe@MIPs QDs) were used to develop a selective and sensitive fluorescent nanosensor for determination of cis-diol-containing flavonoids such as quercetin (Qu), baicalein (Bai) and luteolin (Lut) based on controllable oriented surface imprinting approach. The boronate affinity imprinted silica was used as recognition elements. Under the optimum conditions, the imprinting factor (IF) for Qu, Bai and Lut was evaluated to be 9.42, 6.58 and 10.91, respectively. The results indicated that the boronate affinity quantum dots coated with imprinted silica were successfully prepared. The obtained BA-CdTe@MIPs QDs provided high selectivity and high sensitivity for cis-diol-containing flavonoids such as quercetin and luteolin. The BA-CdTe@MIPs QDs exhibited linear decrease in fluorescence intensity with the increase of concentration of quercetin in the 0.05-25 μM concentration range. The detection limit (LOD) is evaluated to be 0.02 μM. The obtained fluorescent nanosensor could be successfully applied to efficient detection of cis-diol-containing flavonoids in onion skin and human urine samples. The recoveries for the spiked onion skin and urine samples were evaluated to be 83.50-104.00% and 86.67-105.00%, respectively. Clearly, this study provides a rapid and efficient fluorescent detection tool for cis-diol-containing flavonoids in real samples.

Sandwich-Like Sensor for the Highly Specific and Reproducible Detection of Rhodamine 6G on a Surface-Enhanced Raman Scattering Platform

Nonspecificity and low reproducibility are always the main challenges in surface-enhanced Raman scattering (SERS) detection, especially for testing real samples. In this study, we developed a sandwich-like sensor (AuA-pMIP) to detect rhodamine 6G (R6G) by integrating a porous molecularly imprinted polymer (pMIP) with a well-ordered AuNP array (AuA). To form a uniformly distributed hot spot, AuA was fabricated at an oil-water interface and was subsequently fixed between pMIP and a support slide. Finite-difference time-domain simulation indicated that the enhanced electric field covered a distance of ∼2 μm above the AuA, in which the pMIP provided effective mass-transfer channels and sufficient specific binding sites for target molecules. High specificity for AuA-pMIP in R6G detection was demonstrated by comparing the SERS performance of R6G on AuA-pMIP with that of its structural analogues on the same sensor. Remarkably, the stable sandwich-like structure allowed us to achieve a recyclable SERS sensor with high reproducibility. Finally, AuA-pMIP displayed excellent specificity and sensitivity toward R6G in a test based on a real orange juice sample. This study presents a promising method to achieve real sample testing on a SERS platform.

Well-defined hydrophilic "turn-on"-type ratiometric fluorescent molecularly imprinted polymer microspheres for direct and highly selective herbicide optosensing in the undiluted pure milks

Molecularly imprinted polymer (MIP)-based optosensing materials capable of direct, reliable, and highly selective detection of small organic analytes in complex aqueous samples hold great promise in many bioanalytical applications, but their development remains a challenging task. Addressing this issue, well-defined hydrophilic "turn-on"-type ratiometric fluorescent MIP microspheres are developed via a versatile and modular strategy based on the controlled/"living" radical polymerization method. Its general principle was demonstrated by the synthesis of red CdTe quantum dot (QD)-labeled silica particles with surface-bound atom transfer radical polymerization (ATRP)-initiating groups via the one-pot sol-gel reaction and their successive grafting of a thin fluorescent 2,4-D (an organic herbicide)-MIP layer (labeled with green organic fluorophores bearing both nitrobenzoxadiazole (NBD) and urea interacting groups) and hydrophilic poly(glyceryl monomethacrylate) (PGMMA) brushes via surface-initiated ATRP. The introduction of PGMMA brushes and rationally selected dual fluorescence labeling (i.e., red CdTe QDs being inert to 2,4-D and green NBD showing fluorescence "light-up" upon binding 2,4-D) onto MIP particles afforded them excellent complex aqueous sample-compatibility (due to their largely enhanced hydrophilicity) and analyte binding-induced "turn-on"-type ratiometric fluorescence changes, respectively. Such advanced MIP particles proved to be promising optosensing materials, which had a detection limit of 0.13 μM and showed obvious fluorescent color change upon binding different concentrations of 2,4-D in the undiluted pure milk. Moreover, they were successfully applied for direct and highly selective quantification of 2,4-D in the undiluted pure goat and bovine milks with good recoveries (97.9%-104.5%), even in the presence of several analogues of 2,4-D.

Selective Enrichment of Clenbuterol onto Molecularly Imprinted Polymer Microspheres with Tailor-made Structure and Oxygen Functionalities

The noxious clenbuterol misapplied as the feed additive has posed an enormous threat to humans who actively rely on the food chains with high potential of contamination by clenbuterol, such as pork and beef. It is, therefore, highly desirable to develop novel materials and strategies for dealing with the clenbuterol. Herein, functional polymer microspheres prepared by Pickering emulsion polymerization were explored for the selective enrichment of the clenbuterol, and their structure and oxygen functionalities could be tailor-made by a molecular imprinting process. The clenbuterol imprinting was adequately demonstrated to not only increase the particle size (~52 nm vs. ~42 nm) and create cavities for the accommodation of the clenbuterol molecules, but also reduce the oxygen functionalities of the resulting molecularly imprinted polymer microspheres (MIPMs) by approximately 4 at.%, which is believed to correlate with the high specificity of the MIPMs. Various characterization methods were employed to evidence these findings, including scanning electron microscopy, BET measurements, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and elemental mapping examination. More importantly, the MIPMs showed a markedly superior enrichment capability towards clenbuterol to the counterpart, that is, non-molecularly imprinted polymer microspheres (NIPMs). Compared to the NIPMs without specificity for clenbuterol, the MIPMs exhibited an impressive selectivity to clenbuterol, with the relative selectivity coefficient (k') values largely exceeding 1, thus corroborating that the useful molecular imprinting led to the generation of the binding sites complementary to the clenbuterol molecule in the size and functionalities. The MIPMs were also employed as the stationary phase to fabricate molecularly imprinting solid-phase extraction column, and the spike recovery was demonstrated to be not significantly decreased even after nine cycles. Furthermore, the reliability of the method was also evidenced through the comparison of the MIPMs prepared from different batches.

Cuvette-Type LSPR Sensor for Highly Sensitive Detection of Melamine in Infant Formulas

The globalization of food distribution has made necessary to secure safe products to the general consumers through the rapid detection of harmful additives on the field. For this purpose, we developed a cuvette-type localized surface plasmon resonance (LSPR) sensor that can be easily used by consumers with conventional ultraviolet-visible light spectrophotometer for in-situ measurements. Gold nanoparticles were uniformly deposited on a transparent substrate via a self-assembly method to obtain a plasmonically active chip, and the chemical receptor p-nitroaniline (p-NA) was functionalized to stabilize the device sensitivity under external temperature and pH conditions. The fabricated chip was fixed onto a support and combined with a cuvette-type LSPR sensor. To evaluate the applicability of this sensor on the field, sensitivity and quantitative analysis experiments were conducted onto melamine as a model sample from harmful food additives. Under optimal reaction condition (2 mM p-NA for 20 min), we achieved an excellent detection limit (0.01 ppb) and a dynamic range allowing quantitative analysis over a wide concentration range (0.1–1000 ppb) from commercially available milk powder samples.

Semiconductor nanocrystal-polymer hybrid nanomaterials and their application in molecular imprinting

Quantum dots (QDs) are attractive semiconductor fluorescent nanomaterials with remarkable optical and electrical properties. The broad absorption spectra and high stability of QD transducers are advantageous for sensing and bioimaging. Molecular imprinting is a technique for manufacturing synthetic polymeric materials with a high recognition ability towards a target analyte. The high selectivity of the molecularly imprinted polymers (MIPs) is a result of the fabrication process based on the template-tailored polymerization of functional monomers. The three-dimensional cavities formed in the polymer network can serve as the recognition elements of sensors because of their specificity and stability. Appending specific molecularly imprinted layers to QDs is a promising strategy to enhance the stability, sensitivity, and selective fluorescence response of the resulting sensors. By merging the benefits of MIPs and QDs, inventive optical sensors are constructed. In this review, the recent synthetic strategies used for the fabrication of QD nanocrystals emphasizing various approaches to effective functionalization in aqueous environments are discussed followed by a detailed presentation of current advances in QD conjugated MIPs (MIP-QDs). Frontiers in manufacturing of specific imprinted layers of these nanomaterials are presented and factors affecting the specific behaviour of an MIP shell are identified. Finally, current limitations of MIP-QDs are defined and prospects are outlined to amplify the capability of MIP-QDs in future sensing.

A Novel Fluorescence and SPE Adsorption Nanomaterials of Molecularly Imprinted Polymers Based on Quantum Dot-Grafted Covalent Organic Frameworks for the High Selectivity and Sensitivity Detection of Ferulic Acid

A fluorescence and solid phase extraction (SPE) adsorption nanomaterials of molecularly imprinted polymers (MIPs) based on quantum dot-grafted covalent organic frameworks (QD-grafted COFs) was prepared by one-pot surface-imprinting synthesis method. Amino groups of silane reagent were at the surface of QDs to coordinate COFs efficiently by Schiff-base reactions, providing thermal and chemical stability to MIPs. It also reacted with the phenolic hydroxyl groups of ferulic acid (FA) through non-covalent interactions. The nanomaterials were used as fluorescence sensing and SPE adsorption toward determination of ferulic acid. The MIPs based on QD-grafted COFs had good fluorescence response ability, and quenching linearly at concentrations of ferulic acid from 0.03 to 60 mg kg^-1, with a detection limit of 5 µg kg^-1. At the same time, it exhibited a good SPE adsorption ability, and the FA extraction was from 1.63 to 3.11 mg kg^-1 in grain by-products by SPE coupled with high performance liquid chromatography/mass spectrometry (HPLC/MS). The fluorescence and SPE-HPLC/MS were used for the efficient detection of ferulic acid in real samples with recovery values of 88⁻114% and 90⁻97%, respectively. Furthermore, the nanomaterials of MIPs based on QD-grafted COFs were used for FA detection with high sensitivity and selectivity, and it also increased the recycling of waste resources.

Review on Nanomaterial-Based Melamine Detection

Illegal adulteration of milk products by melamine and its analogs has become a threat to the world. In 2008, the misuse of melamine with infant formula caused serious effects on babies of China. Thereafter, the government of China and the US Food and Drug Administration (FDA) limited the use of melamine of 1 mg/kg for infant formula and 2.5 mg/kg for other dairy products. Similarly, the World Health Organization (WHO) has also limited the daily intake of melamine of 0.2 mg/kg body weight per day. Many sensory schemes have been proposed by the scientists for carrying out screening on melamine poisoning. Among them, nanomaterial-based sensing techniques are very promising in terms of real-time applicability. These materials uncover and quantify the melamine by means of diverse mechanisms, such as fluorescence resonance energy transfer (FRET), aggregation, inner filter effect, surface-enhanced Raman scattering (SERS), and self-assembly, etc. Nanomaterials used for the melamine determination include carbon dots, quantum dots, nanocomposites, nanocrystals, nanoclusters, nanoparticles, nanorods, nanowires, and nanotubes. In this review, we summarize and comment on the melamine sensing abilities of these nanomaterials for their suitability and future research directions.

Novel molecularly imprinted polymers on metal–organic frameworks as sensors for the highly selective detection of zearalenone in wheat

This work provides a rapid and simple method for the determination of trace substances in complex systems.

Fluorescence detection of melamine based on inhibiting Cu2+-induced disaggregation of red-emitting silver nanoclusters

Herein, we report a facile method to synthesize red-emitting, water-soluble Ag nanoclusters (Ag NCs) employing lipoic acid as a stabilizing agent. The Ag NCs show aggregation-induced emission property and have good stability and optical properties. Cu²⁺ can disperse the aggregated Ag NCs, accompanied by the quenching of fluorescence. However, the formed Cu²⁺-melamine complex by the coordination chemistry between free copper ion and melamine is able to effectively avoid the quenching process of Cu²⁺ to the Ag NCs. Hence, the Ag NCs can be applied to design a novel fluorescent probe based on this property to detect melamine. In the determination of melamine, the as-prepared fluorescent Ag NCs exhibit favorable sensitivity and high selectivity. The limit of detection (LOD) down to 0.022 mg/L and good recoveries of real sample experiments were obtained. This fluorescent probe is proved to be convenient and rapid for detecting melamine, with potential application to trace melamine analysis in complicated samples.

A nanocomposite optosensor containing carboxylic functionalized multiwall carbon nanotubes and quantum dots incorporated into a molecularly imprinted polymer for highly selective and sensitive detection of ciprofloxacin

A nanocomposite optosensor consisting of carboxylic acid functionalized multiwall carbon nanotubes and CdTe quantum dots embedded inside a molecularly imprinted polymer (COOH@MWCNT-MIP-QDs) was developed for trace ciprofloxacin detection. The COOH@MWCNT-MIP-QDs were synthesized through a facile sol-gel process using ciprofloxacin as a template molecule, 3-aminopropylethoxysilane as a functional monomer and tetraethoxysilane as a cross-linker at a molar ratio of 1:8:20. The synthesized nanocomposite optosensor had high sensitivity, excellent specificity and high binding affinity to ciprofloxacin. Under optimal conditions, the fluorescence intensity of the optosensor decreased in a linear fashion with the concentration of ciprofloxacin and two linear dynamic ranges were obtained, 0.10-1.0 μg L^-1 and 1.0-100.0 μg L^-1 with a very low limit of detection of 0.066 μg L^-1. The imprinting factors of the two linear range were 17.67 and 4.28, respectively. The developed nanocomposite fluorescence probe was applied towards the determination of ciprofloxacin levels in chicken muscle and milk samples with satisfactory recoveries being obtained in the range of 82.6 to 98.4%. The results were also in good agreement with a HPLC method which indicates that the optosensor can be used as a sensitive, selective and rapid method to detect ciprofloxacin in chicken and milk samples.

A molecularly imprinted sensor with enzymatic enhancement of electrochemiluminescence of quantum dots for ultratrace clopyralid determination

A new molecularly imprinted polymer electrochemiluminescence (ECL) sensor was developed for the detection of clopyralid (CPD) based on enzyme-biocatalyzed amplification. CdTe quantum dots were immobilized on the surface of an electrode by reaction with p-aminothiophenol preadsorbed on the electrode. Then a molecularly imprinted film was formed by electrochemical polymerization of o-phenylenediamine in the presence of CPD on the CdTe-modified gold electrode. During the analytical cycle, horseradish peroxidase (HRP)-labeled CPD was replaced by CPD in the sample. The amount of HRP on the molecularly imprinted polymer electrode decreased, and then less H₂O₂ was catalytically decomposed. Subsequently, the ECL intensity of the CdTe-H₂O₂ system was enhanced. There was a good linear relationship between ECL intensity and the concentration of CPD in the range from 2.0 × 10^-11 to 2.5 × 10^-10 mol/L and in the range from 2.5 × 10^-10 to 3.5 × 10^-8 mol/L. The detection limit was 4.1 × 10^-12 mol/L. The sensor was applied to determine CPD in vegetable samples. Graphical abstract A molecularly imprinted electrochemiluminescence sensor was fabricated for ultratrace clopyralid determination. The sensitivity was significantly improved with the enhancement of the ECL intensity of quantum dot via the enzymatic reaction of HRP.

Effects of low-dose melamine exposure during pregnancy on maternal and fetal kidneys in rats

Despite the previous reports on melamine contamination in high concentrations some years ago, there were not many studies on low-level exposure in daily life, particularly in pregnancy. We investigated the effect of low-dose melamine on the kidneys of the pregnant rats and their developing embryos/fetuses during various gestational stages namely implantation, gastrulation, organogenesis, maturation and whole pregnancy. Our results showed that the repeated low level of melamine (12.5, 25, and 50 mg/kg bw/d) during pregnancy did not cause obstruction of renal tubules although more precipitating crystals were found in the early gestational periods. Simple hyperplasia in the maternal tubules and pelvic epithelium were more prominent after exposed to melamine during the whole gestational period. Neonatal kidneys significantly suffered more from congestion in glomeruli and interstitium, dilated tubules and interstitial edema after melamine administration to the mother in the late and the whole gestational periods. A trend of advance of glomerular development in fetuses was also observed. We conclude that in utero exposure of low-level melamine could post a risk on the kidneys of the pregnant mother as well as the developing fetuses, which may further increase the possibility of other health problems later in life.