Nitrogen-doped graphene quantum dots-labeled epitope imprinted polymer with double templates via the metal chelation for specific recognition of cytochrome c

Oriented surface imprinting of epitopes anchored on silica nanoparticles containing quantum dots by thiol-disulfide exchange reactions for the enhanced fluorescence detection of proteins

As artificial receptors for protein recognition, epitope-imprinted polymers combined with fluorescence sensing based on quantum dots (QDs) can be potentially used for biological analysis and disease diagnosis. However, the usual way for fabrication of QD sensors through unoriented epitope imprinting is confronted with the problems of disordered imprinting sites and low template utilization. In this context, a facile and efficient oriented epitope surface imprinting was put forward based on immobilization of the epitope templates via thiol-disulfide exchange reactions. With N-succinimidyl 3-(2-pyridyldithio)-propionate (SPDP) as a heterobifunctional reagent, cysteine-modified epitopes of cytochrome c were anchored on the surface of pyridyl disulfide functionalized silica nanoparticles sandwiching CdTe QDs. After surface imprinting via a sol-gel process, the epitope templates were removed from the surface-imprinted layers simply by reduction of the thiol-disulfide, affording oriented epitope-imprinted sites. By this method, the amount of epitope templates was only 1/20 of traditionally unoriented epitopes. The resulting sensors demonstrated significantly enhanced imprinting performance and high sensitivity, with the imprinting factor increasing from 2.6 to 3.9, and the limit of detection being 91 nM. Such epitope-oriented surface-imprinted method may offer a new design strategy for the construction of high-affinity protein recognition nanomaterials with fluorescence sensing.

Harnessing the Potential of Graphene Quantum Dots for Multifunctional Biomedical Applications

The existing and emerging demand for materials for life and health has contributed to the cultivation and development of respective markets. Nevertheless, the current generation of biomedical materials has yet to fully satisfy the clinical requirements of the market, which is still in its relative infancy. Research and development in this area must be prioritized in light of the pivotal role of new life and health materials in the biological field. Among many life and health materials, GQDs, an emerging nanomaterial, exhibit considerable promise in the biomedical field, primarily due to their exceptional properties. Furthermore, the direct preparation and functionalization of GQDs have facilitated the development of specific functional composites based on GQDs. The biological applications of GQDs are undergoing rapid growth, which makes it necessary to publish a review article presenting the latest advances in this field. This review provides an overview of the significant advances in synthesizing GQDs, the techniques employed for structural characterizations, and the properties that have been elucidated. Furthermore, it presents recent findings on applying GQDs in antimicrobial, anticancer, biosensing, drug delivery, and bioimaging applications. Finally, it explores the potential of GQDs in biomedicine and biotechnology, highlighting the current challenges that remain to be addressed.

Preparation and application of a pseudo-templated multi-monomer aflatoxins imprinted polymer

A functional material was developed with specific recognition properties for aflatoxins for pre-processing enrichment and separation in the detection of aflatoxins in Chinese herbal medicines. In the experiment, ethyl coumarin-3-carboxylate, which has a highly similar structure to the oxonaphthalene o-ketone of aflatoxin, was selected as a pseudo-template, zinc acrylate, neutral red derivative, and methacrylic acid, which have complementary functions, were selected as co-monomers to prepare a pseudo-template multifunctional monomer molecularly imprinted polymer (MIP). The MIP obtained under the optimal preparation conditions has a maximum adsorption capacity of 0.036 mg/mg and an imprinting factor of 3.67. The physical property evaluation of the polymers by Fourier infrared spectrometer, scanning electron microscopy, pore size analyzer, thermogravimetric analyzer, and diffuse reflectance spectroscopy showed that the MIP were successfully prepared and porous spherical-like particles were obtained. The synthesized polymer was used as a solid-phase extraction agent for the separation of aflatoxins from the extract of spina date seed. The linear range of the developed method was 10-1000 ng/mL, the limit of detection was 0.36 ng/mL, the limit of quantification was 1.19 ng/mL, and the recoveries of the extracts at the concentration level of 0.2 μg/mL were in the range 88.0-93.4%, with relative standard deviations (RSDs) of 1.97% (n). The results showed that the preparation of MIPs using ethyl coumarin-3-carboxylate as a template was simple, economical, and convenient. It is expected to become a promising functional material for the enrichment and separation aflatoxins from complex matrices.

Innovations in ion-selective optodes: a comprehensive exploration of modern designs and nanomaterial integration

In recent years, ion-selective optodes (ISOs) have remarkably progressed, driven by innovative modern designs and nanomaterial integration. This review explored the development of modern ISO by describing state-of-the-art strategies to improve their sensitivity, selectivity, and real-time monitoring capacity. The review reported the traditional membrane based-optodes, and investigated the latest research, current design principles, and the use of essential components, such as ionophores, indicator dyes, polymer membranes, and nanomaterials, in ISO fabrication. Special attention was given to nanomaterials (e.g., quantum dots, polymer dots, nanospheres, nanorods and nanocapsules) and particularly on how rare earth elements can further enhance their potential. It also described innovative ISO designs, including wearable optodes, smartphone-based optodes, and disposable paper-based optodes. As the pursuit of highly sensitive, selective, and adaptable ion sensing devices continues, this summary of the current knowledge sets the stage for upcoming innovations and applications in different domains (pharmaceutical formulations, medical diagnosis, environmental monitoring, and industrial applications).

Fabrication of a ratiometric fluorescent probe based on Tb3+ doped dual-emitting carbon dots for the detection of cytochrome c

Cytochrome c (Cyt-c) was commonly an intrinsic biomarker for a variety of cellular characteristics, such as respiration, energy levels, and apoptosis. Herein, a simple fluorescence sensor was constructed for the detection of Cyt-c in buffer and real serum samples. The carbon dots doped with Tb3+ on the premise of 1-(2-pyridylazo)-2-naphthol (PAN) were fabricated and used as a dual-emission ratiometric fluorescent probe for detecting Cyt-c based on the internal filtering effect (IFE). As a fluorescent probe for ultra-sensitive detection, Cyt-c was quantitatively detected at different concentrations from 1 to 1000 nM. The fluorescent detection method for Cyt-c showed a good linear relationship from 1 to 50 nM, and the limit of detection (LOD) was 0.35 nM. In the recovery range of 101.27-103.39 % in human serum samples, the relative standard deviation (RSD) was less than 3.27 % (n = 3). In the end, the possible structures of CDs were predicted by DFT theoretical simulation calculations. All the results proved the ability of carbon dots as fluorescent probes to detect biomarkers and the application prospects in bioanalysis.

Facile fluorescence detection of malachite green in fish using molecularly imprinted polymers doped CdTe quantum dots based system

Malachite green (MG) possesses high toxicity, therefore, the detection of MG in fish tissues is of vital importance. A novel core-shell MIPs doped CdTe quantum dots coated silica nanoparticles (CdTe-MIP/SiO2 NPs) were synthesized via a simple one-pot strategy. The materials were characterized carefully. The resulting CdTe-MIP/SiO2 NPs were coated on the thin layer chromatography plate, and coupled with miniaturized fluorimeter for fluorescence detection of MG in fish samples. The resulting CdTe-MIP/SiO2 NPs based system possessed good linearity (0.01 ∼ 20 μmol/L), high recoveries (98.36 %∼101.45 %) and low detection limit (3.7 nmol/L) for MG. Furthermore, CdTe-MIP/SiO2 NPs based system were employed to measure fish samples spiked with MG, meanwhile, HPLC was utilized to evaluate the accuracy and reliability. And the paired t-test was conducted to evaluate differences between fluorescence method and HPLC, P > 0.05 means no significant difference was observed, the results demonstrated that both fluorescence method and HPLC are suitable for MG analysis.

Epitope imprinted polymeric materials: application in electrochemical detection of disease biomarkers

Epitope imprinting is a promising method for creating specialized recognition sites that resemble natural biorecognition elements. Epitope-imprinted materials have gained a lot of attention recently in a variety of fields, including bioanalysis, drug delivery, and clinical therapy. The vast applications of epitope imprinted polymers are due to the flexibility in choosing monomers, the simplicity in obtaining templates, specificity toward targets, and resistance to harsh environments along with being cost effective in nature. The "epitope imprinting technique," which uses only a tiny subunit of the target as the template during imprinting, offers a way around various drawbacks inherent to biomacromolecule systems i.e., traditional molecular imprinting techniques with regards to the large size of proteins, such as the size, complexity, accessibility, and conformational flexibility of the template. Electrochemical based sensors are proven to be promising tool for the quick, real-time monitoring of biomarkers. This review unravels epitope imprinting techniques, approaches, and strategies and highlights the applicability of these techniques for the electrochemical quantification of biomarkers for timely disease monitoring. In addition, some challenges are discussed along with future prospective developments.

Cellular Therapy Using Epitope-Imprinted Composite Nanoparticles to Remove α-Synuclein from an In Vitro Model

Several degenerative disorders of the central nervous system, including Parkinson’s disease (PD), are related to the pathological aggregation of proteins. Antibodies against toxic disease proteins, such as α-synuclein (SNCA), are therefore being developed as possible therapeutics. In this work, one peptide (YVGSKTKEGVVHGVA) from SNCA was used as the epitope to construct magnetic molecularly imprinted composite nanoparticles (MMIPs). These composite nanoparticles were characterized by dynamic light scattering (DLS), high-performance liquid chromatography (HPLC), isothermal titration calorimetry (ITC), Brunauer–Emmett–Teller (BET) analysis, and superconducting quantum interference device (SQUID) analysis. Finally, the viability of brain endothelial cells that were treated with MMIPs was measured, and the extraction of SNCA from CRISPR/dCas9a-activated HEK293T cells from the in vitro model system was demonstrated for the therapeutic application of MMIPs.

Molecularly Imprinted Polymers in Diagnostics: Accessing Analytes in Biofluids

Bio-applied molecularly imprinted polymers (MIPs) are biomimetic materials with tailor-made synthetic recognition sites, mimicking biological counterparts known for their sensitive and selective analyte detection. MIPs, specifically designed for biomarker analysis...

A high sensitivity electrochemical sensor based on a dual-template molecularly imprinted polymer for simultaneous determination of clenbuterol hydrochloride and ractopamine

A nitrogen-doped Fe-MOF shows a high specific surface area and excellent electrical conductivity after high temperature carbonization. A novel electrochemical sensor based on a N@Fe-MOF@C loaded dual-template molecularly imprinted polymer (DTMIP) modified glassy carbon electrode (GCE) was proposed for the rapid and ultra-sensitive simultaneous detection of clenbuterol hydrochloride (CLB) and ractopamine (RAC). N@Fe-MOF@C combined with a MIP significantly enhanced the electrical signal. Cyclic voltammetry (CV) was used to detect CLB and RAC. The electrochemical polymerization was conducted with O-phenylenediamine as the functional monomer and CLB and RAC as template molecules. The factors affecting the sensor response were optimized. Under the optimal experimental conditions, the CV current response showed a linear range of 10^-12-8 × 10^-9 M for both CLB and RAC, and the detection limit (LOD) for both CLB and RAC was 3.03 × 10^-13 M (S/N = 3). This electrochemical sensing system has high sensitivity, selectivity, excellent reproducibility, repeatability and stability. The recoveries of the actual samples (97.4%-101.2%) and reasonable relative standard deviations (RSDs) (1.06%-3.17%) indicate the practicability of the sensor system. The system has high application value in the rapid detection of CLB and RAC in clenbuterol hydrochloride tablets, human urine and raw pork.

Cobalt-Iron Double Ion-Bovine Serum Albumin Chelation-Assisted Thermo-Sensitive Surface-Imprinted Nanocage with High Specificity

To develop multifunctional protein imprinted materials, a cobalt-iron double ion-BSA directional chelation-assisted thermo-sensitive surface-imprinted hollow nanocage (Co-Fe@CBMA-MIPs) with excellent specificity is developed on the surface of ZIF-67@Co-Fe in this study by synergizing the advantages of surface imprinting, metal ion chelation, anti-protein adsorption segments, and thermo-sensitive components. Beyond previous research, well-designed multifunctional protein-imprinted materials possess high binding capacity, fast adsorption kinetics, and outstanding selectivity. When the adsorption is carried out at 32 °C, the adsorption capacity of Co-Fe@CBMA-MIPs for BSA reaches 520.35 mg/g within 50 min. The imprinting factor is 8.55. The selectivity factors of Co-Fe@CBMA-MIPs for HSA, Bhb, OVA, and Lyz are 3.72, 6.09, 4.10, and 8.41, respectively. More significantly, Co-Fe@CBMA-MIPs could specifically recognize BSA from mixed proteins and actual samples and exhibit excellent repeated use stability. Based on the above advantages, the development of this research provides an effective means to improve the recognition specificity of molecularly imprinted polymers.

The Preparation of CuInS2-ZnS-Glutathione Quantum Dots and Their Application on the Sensitive Determination of Cytochrome c and Imaging of HeLa Cells

Cytochrome c (Cyt c), one of the most significant proteins acting as an electron transporter, plays an important role during the transferring process of the energy in cells. Apoptosis, one of the major forms of cell death, has been associated with various physiological regularity and pathological mechanisms. It was found that Cyt c can be released from mitochondria to cytosol under different pathological conditions, triggering subsequent cell apoptosis. Herein, we developed a fluorescence nanoprobe based on negatively charged CuInS₂-ZnS-GSH quantum dots (QDs) for the sensitive determination of Cyt c. CuInS₂-ZnS-GSH QDs with high photochemical stability and favorable hydrophilicity were prepared by a simple hot reflux method and emit a bright orange-red light. The electron-deficient heme group in Cyt c is affiliated with the electron-rich CuInS₂-ZnS-GSH QDs through the photo-induced electron transfer process, resulting in a large decrease in fluorescence intensity of QDs. A good linearity for concentration of Cyt c in the range of 0.01-7 μmol L^-1 is obtained, and the detection limit of Cyt c is as low as 1.1 nM. The performance on the detection of Cyt c in spiked human serum and fetal bovine serum samples showed good recoveries from 85.5% to 95.0%. Furthermore, CuInS₂-ZnS-GSH QDs were applied for the intracellular imaging in HeLa cells showing an extremely lower toxicity and excellent biocompatibility.

Computational analysis of functional monomers used in molecular imprinting for promising COVID-19 detection

Today, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has recently caused a severe outbreak worldwide. There are still several challenges in COVID-19 diagnoses, such as limited reagents, equipment, and long turnaround times. In this research, we propose to design molecularly imprinted polymers as a novel approach for the rapid and accurate detection of SARS-CoV-2. For this purpose, we investigated molecular interactions between the target spike protein, receptor-binding domain of the virus, and the common functional monomers used in molecular imprinting by a plethora of computational analyses; sequence analysis, molecular docking, and molecular dynamics (MD) simulations. Our results demonstrated that AMPS and IA monomers gave promising results on the SARS-CoV-2 specific TEIYQAGST sequence for further analysis. Therefore, we propose an epitope approach-based synthesis route for specific recognition of SARS-CoV-2 by using AMPS and IA as functional monomers and the peptide fragment of the TEIYQAGST sequence as a template molecule.

Epitope-imprinted polymers: applications in protein recognition and separation

Molecularly imprinted polymers (MIPs) have evolved as promising platforms for specific recognition of proteins. However, molecular imprinting of the whole protein molecule is complicated by its large size, conformational instability, and structural complexity. These inherent limitations can be overcome by using epitope imprinting. Significant breakthroughs in the synthesis and application of epitope-imprinted polymers (EIPs) have been achieved and reported. This review highlights recent advances in epitope imprinting, from the selection of epitope peptide sequences and functional monomers to the methods applied in polymerization and template removal. Technological innovations in detection and extraction of proteins by EIPs are also provided.

Nitrogen and fluorine co-doped green fluorescence carbon dots as a label-free probe for determination of cytochrome c in serum and temperature sensing

As an important biomarker, the analysis of cytochrome c (Cyt c) plays a crucial role in cell-apoptosis or even cancer diagnosis. This work develops a label-free probe for Cyt c using the nitrogen and fluorine co-doped carbon dots (N, F-CDs) which were facile prepared through solvothermal method with 3, 4-difluorophenylhydrazine as precursor. The N, F-CDs have an average diameter of 3.4 nm, and can form a quite stable colloidal solution. The N, F-CDs show bright yellow-green fluorescence, excitation/emission wavelengths 475/530 nm, and a relatively high fluorescence quantum yield of 16.9%. Interestingly, the N, F-CDs indicate a linear and reversible variation of emission intensity with a sensitivity of -1.11% per ℃ in the temperature range from 25 to 60 ℃. Inner filter effect (IFE) between N, F-CDs and Cyt c turns the fluorescence of N, F-CDs from "on" to "off". The sensor possesses the excellent anti-interference ability towards the main components of plasma. Under optimum conditions, there is a linear relationship between fluorescence intensity function (F₀-F) and the concentration of Cyt c in the range of 0.5-25 μΜ with a limit of detection (LOD) (S/N = 3) of 0.25 μM. Finally, the developed method has been successfully used to detect Cyt c in human serum sample with satisfactory recoveries in a range of 93.14-110.40%.

One-step synthesis of fluorescent graphene quantum dots as an effective fluorescence probe for vanillin detection

This study proposes an easy bottom-up method for the synthesis of photoluminescent (PL) graphene quantum dots (GQDs) using citric acid as the carbon source. The obtained GQDs were characterized by high-resolution transmission electron microscopy (HRTEM), UV-vis absorption spectroscopy, fluorescence spectroscopy, and Fourier transform infrared spectroscopy (FT-IR). The synthesised GQDs have an average diameter of 4.76 ± 0.96 nm, with a lattice spacing of 0.24 nm. The GQDs exhibit excitation-independent PL emission. The surface of the GQDs has a variety of functional groups (hydroxyl, carboxyl, and ether groups etc.) to enhance its stability and water solubility. In this study, a fluorescent "on-off" sensor is developed for the selective detection of vanillin in chocolates using GQDs as a fluorescent probe. Under optimal conditions, fluorescence intensity of the GQDs has a good linear relationship with the vanillin concentration (0.0-2.1 × 10-5 mol L-1), with a limit of detection of 2.5 × 10-8 mol L-1. For detection in real samples, the percent recovery of vanillin and the relative standard deviation were 88.0-108.9% and 0.90-5.4%, respectively. Thus, this GQDs-based method has good accuracy and precision and can be used for vanillin detection in practical applications.

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 fluorescent artificial receptor with specific imprinted cavities to selectively detect colistin

A novel and facile fluorescent artificial receptor on the basis of the molecularly imprinted polymer-coated graphene quantum dots was engineered successfully to detect colistin. The colistin imprinted graphene quantum dots (CMIP-GQDs) was synthesized by vinyl-based radical polymerization between functional monomers and crosslinker at around the template molecule on the surface of graphene quantum dots. The size of bare, CNIP-GQDs, and CMIP-GQDs was about 4.8 ± 0.6 nm, 18.4 ± 1.7 nm, and 19.7 ± 1.3 nm, respectively. The CMIP-GQDs, which showed the strong fluorescence emission at 440 nm with the excitation wavelength fixed at 380 nm, had excellent selectivity and specificity to rapidly recognize and detect colistin. The linear range of fluorescence quenching of this fluorescent artificial receptor for detection colistin was 0.016-2.0 μg mL^-1 with a correlation coefficient (R²) of 0.99919, and the detection limit was 7.3 ng mL^-1 in human serum samples. The designed receptor was successfully applied to detect colistin in human serum samples and it achieved excellent recoveries shifted from 93.8 to 105%. Graphical abstract.

An advanced molecularly imprinted electrochemical sensor for the highly sensitive and selective detection and determination of Human IgG

An advanced molecularly imprinted electrochemical sensor with high sensitivity and selectivity for the detection of Human immunoglobulin G (IgG) was successfully constructed. With acrylamide imprinting systems, surface imprinting on the nanoparticles CuFe₂O₄ targeted at IgG was employed to prepare molecularly imprinted polymer, which served as recognition element for the electrochemical sensor. Furthermore, the sensor harnessed a molybdenum disulfide (MoS₂)@nitrogen doped graphene quantum dots (N-GQDs) with ionic liquid (IL) nanocomposite for signal amplification. Under optimized experimental conditions, the sensor shortened the response time to less than 8 min, and the response was linear at the IgG concentration of 0.1-50 ng·mL^-1 with a low detection limit of 0.02 ng·mL^-1 (S/N = 3). Our findings suggested that, the sensor exhibited high detectability and long-time stability. The satisfactory results of human serum sample analysis showed that the developed IgG sensor had promising potential clinical applications in detecting IgG content.

Cancer biomarker detection in human serum samples using nanoparticle decorated epitope-mediated hybrid MIP

The determination of disease-associated molecules at trace amounts is a key factor for early and efficient diagnosis from human body fluids. Herein, an ultrasensitive electrochemical sensor based on hybrid epitope imprinting and nanomaterial amplification was developed. The hybrid epitope imprinting was achieved by electropolymerization in the presence of two computationally selected and cysteine modified epitopes of neuron specific enolase (NSE), as-synthesized gold nanoparticles (AuNPs), and functional monomer. The AuNPs decorated epitope-mediated hybrid MIPs, as well as the standard hybrid MIPs, were utilized for the preparation of electrochemical sensors to demonstrate the impact of nanomaterial's modification in the polymer network for biomarker sensing. The fabrication process of both sensor types was investigated by employing cyclic voltammetry, square wave voltammetry, atomic force microscopy, and scanning electron microscopy. The biomarker assay using the standard hybrid MIPs resulted in 2.5-fold higher sensitivity compared to single epitope imprints, whereas the AuNP-hybrid MIPs enhanced the sensitivity level to a great extent and allowed the recognition of NSE in human serum in a concentration range of 25-4000 pg/mL. Comparative selectivity studies with non-imprinted polymer resulted in an imprinting factor of 4.2, confirming the high target selectivity of AuNP-MIP cavities. Cross-reaction of the sensor with four reference molecules (dopamine, bovine serum albumin, glucose and elongated peptide) was negligible. As compared to current strategies for epitope imprinting which rely on single epitopes for the formation of molecular cavities, the hybrid epitope-MIPs, particularly with the inclusion of AuNPs have provided more desirable sensing platforms with high sensitivity, affinity and specificity.

Tumor-Sensitive Biodegradable Nanoparticles of Molecularly Imprinted Polymer-Stabilized Fluorescent Zeolitic Imidazolate Framework-8 for Targeted Imaging and Drug Delivery

Targeting enrichment of nanocarriers at tumor sites and effective drug release are critical in cancer treatment. Accordingly, we used fluorescent zeolitic imidazolate framework-8 nanoparticles loaded with doxorubicin (FZIF-8/DOX) as the core and a molecularly imprinted polymer (MIP) as the shell to synthesize tumor-sensitive biodegradable FZIF-8/DOX-MIP nanoparticles (FZIF-8/DOX-MIPs). The MIP prepared with the epitope of CD59 cell membrane glycoprotein as the template allowed FZIF-8/DOX-MIPs to be enriched to tumor sites by actively targeting recognition of MCF-7 cancer cells (CD59-positive). Moreover, using N,N'-diacrylylcystamine as the cross-linker and dimethylaminoethyl methacrylate as the main monomer, the MIP's framework will be broken under the stimulation of a tumor microenvironment (high-concentration glutathione and weakly acidic), so that the internal FZIF-8/DOX is exposed to a microacidic environment to release DOX through further degradation. More importantly, the ability of FZIF-8/DOX-MIPs in targeted fluorescence imaging and effective drug release has been validated both in vitro and in vivo. Compared to other cells and nanoparticles, FZIF-8/DOX-MIPs were more capable of being phagocytosed by MCF-7 cells and were more lethal to MCF-7 cells. In the comparative experiments carried out on tumor-bearing mice, FZIF-8/DOX-MIPs had the best inhibitory effect on the growth of MCF-7 tumors. Furthermore, the FZIF-8/DOX-MIPs can serve as a diagnostic agent because of the active targeting of MCF-7 cells and the stronger red fluorescence of the embedded carbon quantum dots. Because of the active targeting ability, good biocompatibility, tumor-sensitive biodegradability, and effective drug release performance, FZIF-8/DOX-MIPs can be widely used in tumor imaging and treatment.

Rational construction of a triple emission molecular imprinting sensor for accurate naked-eye detection of folic acid

Multiple emissions of blue, green and red from a molecular imprinting sensor rationally constructed, were used for the fluorescence colorimetric visualization of a fluorescent analyte of folic acid, using a flexible post-imprinting mixing strategy. That is, two kinds of folic acid-templated molecularly imprinted polymers (MIPs) were firstly synthesized by encapsulating green and red fluorescent quantum dots (g-QDs and r-QDs) individually on SiO2 cores, and they were then mixed at an appropriate ratio, resulting in a triple emission MIPs sensor. Upon folic acid recognition, the inherent blue fluorescence of folic acid was intensified, and the green and red fluorescence of the sensor QDs were gradually quenched. The quenching rate difference between g-QDs and r-QDs was greatly enhanced and used to obtain a wider-range and profuse fluorescence color evolution, by investigating the influences of the QDs modifier, eluent and imprinting layer thickness in detail. Under optimal conditions, the ratiometric intensity change of the three color emissions varied in a logistic function within 0.01-50 ppm of folic acid, and the corresponding fluorescence colors shifted from yellow to orange to red to purple and finally to blue. This excellent visualization capability of the MIPs sensor contributed to the accurate naked-eye detection of folic acid concentration using a portable ultraviolet lamp. Moreover, the MIPs sensor succeeded in determining folic acid in complicated food and serum samples, providing comparable results with the PRC standard method and satisfactory recoveries of 99.5-108.0%. The merits, including construction simplicity, high sensitivity and selectivity, and result visualization, enable such a multiple emission MIPs sensing strategy to be potentially applicable for visual identification and determination of various analytes in more fields.

Applications of Graphene Quantum Dots in Biomedical Sensors

Due to the proliferative cancer rates, cardiovascular diseases, neurodegenerative disorders, autoimmune diseases and a plethora of infections across the globe, it is essential to introduce strategies that can rapidly and specifically detect the ultralow concentrations of relevant biomarkers, pathogens, toxins and pharmaceuticals in biological matrices. Considering these pathophysiologies, various research works have become necessary to fabricate biosensors for their early diagnosis and treatment, using nanomaterials like quantum dots (QDs). These nanomaterials effectively ameliorate the sensor performance with respect to their reproducibility, selectivity as well as sensitivity. In particular, graphene quantum dots (GQDs), which are ideally graphene fragments of nanometer size, constitute discrete features such as acting as attractive fluorophores and excellent electro-catalysts owing to their photo-stability, water-solubility, biocompatibility, non-toxicity and lucrativeness that make them favorable candidates for a wide range of novel biomedical applications. Herein, we reviewed about 300 biomedical studies reported over the last five years which entail the state of art as well as some pioneering ideas with respect to the prominent role of GQDs, especially in the development of optical, electrochemical and photoelectrochemical biosensors. Additionally, we outline the ideal properties of GQDs, their eclectic methods of synthesis, and the general principle behind several biosensing techniques.

Visual Simultaneous Detection of Hepatitis A and B Viruses Based on a Multifunctional Molecularly Imprinted Fluorescence Sensor

Simultaneous detection of large viruses has been a great obstacle in the field of molecular imprinting. In this work, for the first time, a multifunctional molecularly imprinted sensor for single or simultaneous determination of hepatitis A virus (HAV) and hepatitis B virus (HBV) is provided. Visual detection was realized due to the color of green and red quantum dots that varied with the concentration of the target substance. The combination of hydrophilic monomers and metal chelation reduced the nonspecific binding and enhanced the specificity of adsorption. As a result, satisfactory selectivity and sensitivity were obtained for the detection of the two viruses, with imprinting factors of 3.70 and 3.35 for HAV and HBV, and limits of detection of 3.4 and 5.3 pmol/L, respectively, that were achieved within 20 min. The excellent recoveries during simultaneous detection and single detection modes indicate the prominent ability of the proposed sensor to detect HAV and HBV in human serum and the potential ability to simultaneously detect multiple viruses in real applications.

A label-free RTP sensor based on aptamer/quantum dot nanocomposites for cytochrome c detection

Given the outstanding room-temperature phosphorescence (RTP) of Mn–ZnS quantum dots (QDs) and the specific recognition performance of the aptamer, we built phosphorescent composites from aptamers conjugated with polyethyleneimine quantum dots (PEI-QDs) and applied them to cytochrome c (Cyt c) detection. Specifically, QDs/CBA composites were generated from the electrostatic interaction between the positively-charged PEI-QDs and the negatively-charged Cyt c binding aptamer (CBA). With the presence of Cyt c, the Cyt c can specifically bind with the QDs/CBA composites, and quench the RTP of QDs through photoinduced electron-transfer (PIET). Thereby, an optical biosensor for Cyt c detection was built, which had a detection range of 0.166–9.96 μM and a detection limit of 0.084 μM. This aptamer-mediated phosphorescent sensor with high specificity and operational simplicity can effectively avoid the interference of scattering light from complex substrates. Our findings offer a new clue for building biosensors based on QDs and aptamers.

In this study, the nanocomposites from polyethyleneimine-capped Mn-doped ZnS QDs (PEI-QDs) and Cyt c binding aptamer (CBA) were prepared and used as Cyt c RTP sensors..

Highly Effective Drug Delivery and Cell Imaging Using Fluorescent Double-Imprinted Nanoparticles by Targeting Recognition of the Epitope of Membrane Protein

Nanocarriers with both targeting ability and stable loading of drugs can more effectively deliver drugs to precise tumor sites for therapeutic effects. Accordingly, we have rationally designed fluorescent molecularly imprinted polymer nanoparticles (FMIPs), which use N-terminal epitope of P32 membrane protein as the primary template and doxorubicin (DOX) as the secondary template. The DOX imprinted cavity can stably carry the drug and the epitope-imprinted cavity allows FMIPs to actively recognize the P32-positive 4T1 cancer cells. The targeted therapeutic effect of DOX-loaded FMIPs (FMIPs@DOX) is investigated in vitro and in vivo. The FMIPs@DOX only causes apoptosis in 4T1 cancer cells compared to C8161 cells (expressing low level of P32). In addition, highly effective inhibition of 4T1 malignant breast tumors using FMIPs@DOX is achieved in the model of tumor-bearing mice. Importantly, the antitumor effect achieved by intravenous injection of FMIPs@DOX is almost identical to that by intratumoral injection. Furthermore, the FMIPs can serve as a targeted fluorescence imaging agent due to the high specificity of the epitope-imprinted cavity and the stable fluorescence of the embedded silicon nanoparticles. These results demonstrate the effectiveness of the FMIPs for active targeted drug delivery and imaging. Furthermore, the FMIPs provide a direction for drug-loaded nanocarrier.

Preparation of Dual-Template Epitope Imprinted Polymers for Targeted Fluorescence Imaging and Targeted Drug Delivery to Pancreatic Cancer BxPC-3 Cells

Molecularly imprinted polymers were commonly used for drug delivery. However, single-template molecularly imprinted polymers often fail to achieve both drug delivery and precise targeting. To address this issue, a dual-template molecularly imprinted polymer nanoparticle used for targeted diagnosis and drug delivery for pancreatic cancer BxPC-3 cells (FH-MIPNPs) was prepared. In the FH-MIPNPs, the 71-80 peptide of human fibroblast growth-factor-inducible 14 modified with glucose (Glu-FH) and bleomycin (BLM) were used as templates simultaneously, so that the FH-MIPNPs could load BLM and bind to the BxPC-3 cells, which overexpress human fibroblast growth-factor-inducible 14 (FN14). Targeted imaging experiments in vitro show that the FH-MIPNPs could specifically target BxPC-3 cells and that there is no targeting effect on cells without expression of FN14. In vivo antitumor experiment results demonstrated that the FH-MIPNP-loaded BLM (FH-MIPNPs/BLM) could inhibit the growth of xenografts tumor of BxPC-3 (tumor volume increased to 1.05×), which shows that FH-MIPNPs/BLM had obvious targeted therapeutic effect compared to the other three control groups of BLM, FH-NIPNPs/BLM, and physiological saline (tumor volume increased to 1.5×, 1.6×, and 2.4×, respectively). What is more, FH-MIPNPs have low biotoxicity through toxicity experiments in vitro and in vivo, which is favorable toward making molecularly imprinted polymers an effective platform for tumor-targeted imaging and therapy.

Fluorescent probe based on carbon dots/silica/molecularly imprinted polymer for lysozyme detection and cell imaging

The abnormal concentration of lysozyme in body fluids and tissues is a potential indicator for diseases such as leukemia and meningitis. In this work, by combining the excellent optical properties of carbon dots (CDs) with the favorable selectivity of molecularly imprinted polymer (MIP), a novel fluorescent probe for lysozyme detection and cell imaging was constructed, where silanized CDs with low cytotoxicity (CDs/SiO₂) were used as the fluorescence signal reporter and N-isopropylacrylamide (NIPAM) was used as the temperature-sensitive monomer. The as-prepared CDs/SiO₂/MIP showed a thermo-sensitive property for the response to lysozyme. Moreover, this probe could be used for quantitative detection of lysozyme, with a wider detection range (0.001~0.01 mg/mL), a low detection limit (0.55 μg/mL), and a high selectivity. Importantly, the MTT assay testified that the fluorescent CDs/SiO₂/MIP probe had low cytotoxicity. In addition, human hepatoma carcinoma cells (HepG-2 cells) could be stained by the CDs/SiO₂/MIP, and showed a bright intracellular green fluorescence, indicating that the imaging of live cells was possible. This study provides a new way to detect lysozyme in vitro and an attractive perspective to probe intracellular lysozyme in vivo.

Advances in Molecularly Imprinting Technology for Bioanalytical Applications

In recent years, along with the rapid development of relevant biological fields, there has been a tremendous motivation to combine molecular imprinting technology (MIT) with biosensing. In this situation, bioprobes and biosensors based on molecularly imprinted polymers (MIPs) have emerged as a reliable candidate for a comprehensive range of applications, from biomolecule detection to drug tracking. Unlike their precursors such as classic immunosensors based on antibody binding and natural receptor elements, MIPs create complementary cavities with stronger binding affinity, while their intrinsic artificial polymers facilitate their use in harsh environments. The major objective of this work is to review recent MIP bioprobes and biosensors, especially those used for biomolecules and drugs. In this review, MIP bioprobes and biosensors are categorized by sensing method, including optical sensing, electrochemical sensing, gravimetric sensing and magnetic sensing, respectively. The working mechanism(s) of each sensing method are thoroughly discussed. Moreover, this work aims to present the cutting-edge structures and modifiers offering higher properties and performances, and clearly point out recent efforts dedicated to introduce multi-sensing and multi-functional MIP bioprobes and biosensors applicable to interdisciplinary fields.

Specific quantification of atropine using molecularly imprinted polymer on graphene quantum dots

Herein, development of a reliable and specific fluorometric assay was disclosed for the sensitive detection of atropine. The method was designed using the surface molecularly imprinted polymer on high fluorescent graphene quantum dots (GQDs). Molecularly imprinted polymer capped GQDs (MIP-GQDs) were prepared through the common co-polymerization reaction of 3-(3-aminopropyl) triethoxysilane (APTES) and tetraethyl orthosilicate (TEOS), act as the main functional and cross-linking monomers, respectively. The used template for this reaction was atropine. The created blue luminescent MIP-GQDs composite, which had a great affinity to adsorb atropine from the sample solution, could lead to a notable fluorescence quenching. In fact, GQDs act as the recognizing antenna for adsorbed atropine into the specific MIP sites. The linear association between the observed quenching effect and atropine concentration was exploited to design a selective assay to the detection of atropine. After optimization process, a linear calibration graph was achieved in the atropine concentration range of 0.5-300 ng mL^-1 with a detection limit of 0.22 ng mL^-1. Exploitation of high specific MIP technique along with high fluorescent GQDs provided a highly selective and sensitive assay for atropine as a model analyte. It was adequately utilized for the analysis of atropine in biological samples.

Molecularly Imprinted Polymers in Electrochemical and Optical Sensors

Molecular imprinting is the process of template-induced formation of specific recognition sites in a polymer. Synthetic receptors prepared using molecular imprinting possess a unique combination of properties such as robustness, high affinity, specificity, and low-cost production, which makes them attractive alternatives to natural receptors. Improvements in polymer science and nanotechnology have contributed to enhanced performance of molecularly imprinted polymer (MIP) sensors. Encouragingly, recent years have seen an increase in high-quality publications describing MIP sensors for the determination of biomolecules, drugs of abuse, and explosives, driving toward applications of this technology in medical and forensic diagnostics. This review aims to provide a focused overview of the latest achievements made in MIP-based sensor technology, with emphasis on research toward real-life applications.

Fluorescence alteration of MPA capped CdSe quantum dots by spontaneous biomarker protein adsorption

Quantum dots (QDs) have significant potentials in biomedical applications of bioimaging and biosensing. Spontaneous adsorption of proteins on QDs surface is a common phenomenon, which occurred to serum proteins in biological samples, and has been observed to enhance QDs fluorescence. In this study, fluorescence alteration of 3-mercaptopropionic acid (MPA) capped CdSe quantum dots by four individual biomarker proteins was investigated. By monitoring the fluorescence emission of QDs, the biomarker protein adsorbed spontaneously on QDs surface was recognized and quantified. When alpha fetoprotein (AFP) or heat shock protein 90 alpha (HSP90α) were present, the QDs became brighter. The presence of cytochrome C (CytoC) or lysozyme (Lyz) made the QDs dimmer first, and then brighter. Within five minutes response time all four biomarker proteins were detected individually with the estimated detection limit in the range of 1-10 ng/mL and good linear dynamic ranges. The results suggested that the fluorescence of QDs was responsive to not only serum proteins but also biomarker proteins. The fluorescence response was able to correlate quantitatively with the amount of biomarker proteins in relatively low concentrations. These results provide more information to understand QDs and support their applications in biomedical fields.

Phosphate-imprinted magnetic nanoparticles using phenylphosphonic acid as a template for excellent recognition of tyrosine phosphopeptides

The tyrosine phosphorylation of proteins and peptides plays a vital role in cell signal transduction pathways, and it is very important to assay them for understanding their action mechanism. Due to the low levels of the tyrosine phosphopeptides (pTyr) in cells, it is a challenge to enrich them with traditional sorbents, therefore, development of specific and selective sorbents is urgent and necessary. In this work, the phosphate-imprinted magnetic nanoparticles (PMNPs) to enrich the pTyr with high efficiency and selectivity have been fabricated using the phenylphosphonic acid as a template for the "epitope" of pTyr. The magnetic nanoparticles have been functionalized with TiO₂ and then the imprinting silica shells have been coated on the surface of the functional core to obtain the PMNPs sorbents. The PMNPs can obviously shorten the enrichment time and improve the adsorption efficiency for pTyr, and the epitope imprinting films provide an excellent selective recognition ability to target. The recognition capability of PMNPs for pTyr is 90.3 μg/mg and the imprinting factor of the sorbents can reach 24.4. The results indicate that the PMNPs can enrich the pTyr from the tryptic digest of β-casein samples with high specificity, and the spiking recoveries of the pTyr range from 85.1% to 93.8% with the RSD from 0.04 to 3.73. With the high adsorption capacity, rapid separation, excellent specificity and recyclability, the PMNPs sorbents show great potential for analysis of the phosphorylation of peptides in biological and medical fields.

Label-free fluorescence imaging of cytochrome c in living systems and anti-cancer drug screening with nitrogen doped carbon quantum dots

As an important biomarker for the early stage of apoptosis, cytochrome c (Cyt c) has been recognized as a key component of the intrinsic apoptotic pathway. Fluorescence imaging tools enabling detection of Cyt c in apoptotic signaling have been rarely explored, though they are critical for cell biology and clinical theranostics. Here, we designed a novel label-free N-doped carbon dot (N-doped CD)-based nanosensor that enables fluorescence activation imaging of Cyt c release in cell apoptosis. The inner filter effect of Cyt c towards N-doped CDs enabled quantitative Cyt c measurement. The nanosensor exhibited high sensitivity and selectivity, rapid response, good cell-membrane permeability and low cytotoxicity. All these features are favorable for in situ visualization of Cyt c for apoptosis research. Notably, the developed nanosensor was successfully applied to monitor intracellular release of Cyt c, and to visualize Cyt c in living zebrafish for the first time. Moreover, it also provided a viable platform for cell-based screening of apoptosis-inducing compounds. In virtue of these advantages and potential, the developed assay not only holds great significance for the better understanding of certain diseases at the cellular level, but also provides an invaluable platform for apoptotic studies and screening of anti-cancer drugs toward drug development.

Novel surface imprinted magnetic mesoporous silica as artificial antibodies for efficient discovery and capture of candidate nNOS–PSD-95 uncouplers for stroke treatment

Magnetic mesoporous silica imprinted materials as artificial antibodies for the discovery and capture of candidate nNOS–PSD-95 uncouplers for stroke treatment.

A novel fluorescence strategy for mercury ion and trypsin activity assay based on nitrogen-doped graphene quantum dots

Fluorescent detection of Hg²⁺ and trypsin based on trypsin-modulated competition between Hg²⁺, N-GQDs and HSA.

Sustained and Cost Effective Silver Substrate for Surface Enhanced Raman Spectroscopy Based Biosensing

While surface enhanced Raman spectroscopy (SERS) based biosensing has demonstrated great potential for point-of-care diagnostics in the laboratory, its application in the field is limited by the short life time of commonly used silver based SERS active substrates. In this work, we report our attempt towards SERS based field biosensing, involving the development of a novel sustained and cost-effective substrate composed of silver nanoparticles protected by small nitrogen-doped Graphene Quantum Dots, i.e. Ag NP@N-GQD, and its systematic evaluation for glucose sensing. The new substrate demonstrated significantly stronger Raman enhancement compared to pure silver nanoparticles. More importantly, the new substrate preserved SERS performance in a normal indoor environment for at least 30 days in both the wet and dry states, in contrast to only 10 days for pure silver nanoparticles. The Ag NP@N-GQD thin film in the dry state was then successfully applied as a SERS substrate for glucose detection in mouse blood samples. The new substrate was synthesized under mild experimental conditions, and the cost increase due to N-GQD was negligible. These results suggest that the Ag NP@N-GQD is a cost-effective and sustained SERS substrate, the development of which represents an important step towards SERS based field biosensing.

Imprinting Technology in Electrochemical Biomimetic Sensors

Biosensors are a promising tool offering the possibility of low cost and fast analytical screening in point-of-care diagnostics and for on-site detection in the field. Most biosensors in routine use ensure their selectivity/specificity by including natural receptors as biorecognition element. These materials are however too expensive and hard to obtain for every biochemical molecule of interest in environmental and clinical practice. Molecularly imprinted polymers have emerged through time as an alternative to natural antibodies in biosensors. In theory, these materials are stable and robust, presenting much higher capacity to resist to harsher conditions of pH, temperature, pressure or organic solvents. In addition, these synthetic materials are much cheaper than their natural counterparts while offering equivalent affinity and sensitivity in the molecular recognition of the target analyte. Imprinting technology and biosensors have met quite recently, relying mostly on electrochemical detection and enabling a direct reading of different analytes, while promoting significant advances in various fields of use. Thus, this review encompasses such developments and describes a general overview for building promising biomimetic materials as biorecognition elements in electrochemical sensors. It includes different molecular imprinting strategies such as the choice of polymer material, imprinting methodology and assembly on the transduction platform. Their interface with the most recent nanostructured supports acting as standard conductive materials within electrochemical biomimetic sensors is pointed out.