An “on-off” Electrochemiluminescence Biosensor Based on Molecularly Imprinted Polymer and Recycling Amplifications for Determination of Dopamine

A sensitive "off-on" electrochemiluminescence DNA sensor based on signal cascade amplification circuit and distance-dependent energy transfer

A sensitive "off-on" electrochemiluminescence (ECL) DNA sensor was constructed based on Exo III-assisted cascade amplification system. In the cascade amplification circuit, target DNA and Exo III cutting substrate were designed into an inverted T-shaped binding mode to form a stable DNA junction, thus effectively triggering Exo III digestion cycle. During the biosensor assembly process, ferrocene (Fc) and distance-dependent ECL resonance energy transfer (ECL-RET) and surface plasmon resonance (SPR) effects were introduced to regulate the ECL of semiconductor quantum dots (QDs). Carboxylated ZnCdSe/ZnS QDs were used as ECL signal probes and K2S2O8 was coreactant, and the initial cathodic ECL signal of QDs was efficiently quenched through electron and energy transfer with Fc and ECL-RET with Au NPs, leaving the system in "off" state. After the products of cascade amplification were introduced into the electrode surface, the single-stranded DNA modified with Fc was displaced, and the distance between Au NPs and QDs became farther, resulting in a transition from ECL-RET to SPR, and then a significant ECL signal boost was achieved, turning the system into "on" state. The combination of efficient cascade amplification system and sensitive "off-on" ECL signal change mode enabled the biosensing platform to detect target DNA with high selectivity (able to distinguish single-base mutated DNA) and ultra-high sensitivity (limit of detection was 31.67 aM, S/N = 3), providing a new perspective for designing highly sensitive and programmable ECL biosensors.

Stable and reproducible MIP-ECL sensors for ultra-sensitive and accurate quantitative detection of Estrone

Estrone (E1), as an endogenous estrogen, has a variety of physiological functions in human body and is of great significance to human health. On the other hand, it is a widely distributed and highly disturbing environmental endocrine disruptor in water. Therefore, there is an urgent need to develop a sensitive, rapid, and inexpensive method for the on-site determination of E1, which is not only for clinical diagnosis and treatment, but also for the investigation and monitoring of endogenous estrogen pollution in environmental water. In this study, Ru(bpy)3 2+/MWCNTs/Nafion/gold electrodes were prepared by surface electrostatic adsorption and ion exchange. A molecularly imprinted membrane (MIP) with the capability to recognize E1 molecules was prepared by sol-gel method, and the electrodes were modified with MIP to form an electrochemical luminescence sensor (MIP-ECL). This method simultaneously possesses ECL's advantage of high sensitivity and MIP's advantage of high selectivity. Moreover, the addition of carboxylated multi-walled carbon nanotubes (MWCNT-COOH) improved the functionalization of the gold electrode surface and increased the binding sites of MIP. Meanwhile, the good conductivity of MWCNTs promoted electron transfer and further improved the sensitivity of the sensor. The sensor showed a wide linear interval in which the E1 concentrations can range from 0.1 μg/L to 200 μg/L, along with a high linear correlation coefficient (R 2 = 0.999). The linear regression equation of the sensor was Y = 243.64x-79.989, and the detection limit (LOD) was 0.0047 μg/L. To validate our sensor, actual samples were also measured by the reference method (LC-MS/MS), and it was found that the relative deviation of quantitative results of the two different methods was less than 4.1%. This indicates that the quantitative results obtained by this sensor are accurate and can be used for rapid in situ determination of E1 in clinical samples and environmental water.

A dual-recognition MIP-ECL sensor based on boric acid functional carbon dots for detection of dopamine

We report a molecularly imprinted polymer electrochemiluminescence (MIP-ECL) sensor with dual recognition effects on dopamine (DA). Boric-acid-functionalized carbon dots (B-CDs) with good ECL performance at - 2.0 V (vs. Ag/AgCl) were prepared and immobilized on a glassy carbon electrode (GCE). The MIP was then introduced via electropolymerization using o-phenylenediamine (OPD) as a functional monomer and DA as a template molecule to fabricate the MIP-ECL sensor. The cavities in the MIP after elution were used to capture the target molecular DA. The affinity of boric acid of B-CDs to the cis-diol of DA, as well as the special recognition of MIP, provides dual recognition effects on DA. The selective readsorption of DA onto the sensor leads to the ECL quenching of B-CDs. The quenching effect was used to detect DA from 1.0 × 10^-9 to 1.0 × 10^-5 mol·L^-1 with a detection limit of 2.1 × 10^-10 mol·L^-1. The dual recognition caused the MIP-ECL sensor exhibiting excellent selectivity and sensitivity toward  DA. The sensor was successfully used to determine DA in real samples.

Ultrasensitive electrochemiluminescence sensor based on perovskite quantum dots coated with molecularly imprinted polymer for prometryn determination

A highly effective molecularly imprinted electrochemiluminescence sensor was constructed for prometryn determination in environmental and biological samples by using perovskite quantum dots coated with a molecularly imprinted silica layer (MIP/CsPbBr₃-QDs) as the recognition and response element. MIP/CsPbBr₃-QDs were immobilized on a glassy carbon electrode (GCE) through electropolymerization, and the electrochemiluminescence (ECL) response of MIP/CsPbBr₃-QDs could be motivated under the condition of H₂O₂ as co-reactant. ECL signal was selectively quenched with prometryn by hindering electron transfer and directly proportional to the logarithm of prometryn concentration (0.10-500.0 μg/L) with a correlation coefficient of 0.9960. Limits of detection in fish and seawater samples were 0.010 μg/kg and 0.050 μg/L, respectively. Excellent recoveries of 88.0%-106.0% were acquired for fish and seawater samples with a relative standard deviation below 4.2%. The constructed MIECL sensor based on MIP/CsPbBr₃-QDs showed good stability, accuracy, and precision for sensitive detection of prometryn in aquaculture products and environmental samples.

Large-Area Interfaces for Single-Molecule Label-free Bioelectronic Detection

Bioelectronic transducing surfaces that are nanometric in size have been the main route to detect single molecules. Though enabling the study of rarer events, such methodologies are not suited to assay at concentrations below the nanomolar level. Bioelectronic field-effect-transistors with a wide (μm²-mm²) transducing interface are also assumed to be not suited, because the molecule to be detected is orders of magnitude smaller than the transducing surface. Indeed, it is like seeing changes on the surface of a one-kilometer-wide pond when a droplet of water falls on it. However, it is a fact that a number of large-area transistors have been shown to detect at a limit of detection lower than femtomolar; they are also fast and hence innately suitable for point-of-care applications. This review critically discusses key elements, such as sensing materials, FET-structures, and target molecules that can be selectively assayed. The amplification effects enabling extremely sensitive large-area bioelectronic sensing are also addressed.

Selective detection of enrofloxacin in biological and environmental samples using a molecularly imprinted electrochemiluminescence sensor based on functionalized copper nanoclusters

Enrofloxacin (ENR) is a broad-spectrum fungicide that has been largely applied in pharmacy and animal-specific medicine. In this paper, a simple, novel and highly sensitive molecularly imprinted electrochemiluminescence (MIP-ECL) sensor based on mercaptopropionic acid-functionalized copper nanoclusters (MPA-Cu NCs) was developed to selectively detect enrofloxacin (ENR). MPA-Cu NCs prepared by a one-step method were used to modify the glassy carbon electrode. A molecularly imprinted polymer film containing the cavity was constructed after electropolymerization and elution. Under optimized conditions, the MIP-ECL sensor could detect ENR in the range of 0.1 nM-1 μM (R² = 0.9863) with a low limit of detection of 27 pM, and the recovery rates of ENR in biological and lake water samples were 88.20-105.0%. The MIP-ECL sensor provided path to improve the stability issues of Cu NCs, which might open promising avenues to develop new ECL systems for biological analysis and environmental water monitoring.

A Fenton-like reaction system with analyte-activated catfish effect as an enhanced colorimetric and photothermal dopamine bioassay

Fenton-like reaction systems have been proven to be efficient as powerful promoters in advanced oxidation processes (AOPs) due to their generated reactive oxygen species (ROS), such as ˙OH and ˙O₂^-, which can further oxidize a specific chromogenic substrate like 3,3',5,5'-tetramethylbenzidine (TMB) to generate sensitive color readout and thereby demonstrate more potential in the colorimetric analysis field. However, the inherent drawback of the low rate-limiting step of Fe³⁺/Fe²⁺ conversion in the Fenton-like reaction and its resultant inefficiency for H₂O₂ decomposition hinder its practical applications. We herein communicate an analyte-activated catfish effect based catalysis strategy to promote the Fenton-like reaction, in which dopamine, like a catfish, was added to activate the Fenton-like reaction. By definition, the conversion rate of Fe³⁺ to Fe²⁺ in the proposed Fenton-like reaction can be significantly accelerated through a specific DA-mediated electron transfer process which further promotes the reaction activity in the Fenton-like reaction to generate more ˙OH and ˙O₂^- radicals. As a result, the produced ˙OH and ˙O₂^- radicals in such a reaction system can significantly oxidize TMB indicator into its oxidation product (TMBox) and therefore indicate the corresponding target-dependent color and photothermal signal readout, enabling the successful fabrication of a more sensitive and stable colorimetric and photothermometric DA sensor. More significantly, this strategy can greatly advance the practical application of Fenton-like reactions in the fields of colorimetric and photothermometric bioassays.

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 molecularly imprinted electrochemiluminescence nanoprobe based on complexes consisting of CdTe and multiwall carbon nanotube for sensitive determination of clenbuterol

An electrochemiluminescence (ECL) nanoprobe was fabricated for the determination of clenbuterol (CLB). A molecularly imprinted polymer (MIP) film was coated on the surface of the glassy carbon electrode modified with CdTe-doped multiwall carbon nanotubes. The MIP film with CLB as the template molecule improves the selectivity of the nanoprobe, CdTe is used as ECL signal amplifier, and MWCNT works as the carrier. The ECL intensity is altered by elution and reabsorption of CLB. The possible reaction mechanism and experimental parameters of the nanoprobe are discussed. Under optimized conditions, the quenched ECL intensity and the CLB concentration have a linear relationship in the range 2.3 × 10^-9 to 1.5 × 10^-5 mol·L^-1, and the detection limit is 1.0 × 10^-9 mol·L^-1 (S/N = 3). The nanoprobe was successfully applied to the determination of CLB in pork samples. Graphical abstract Schematic representation of the molecularly imprinted electrochemiluminescence nanoprobe based on complexes consisting of CdTe and multiwall carbon nanotube used to determinate clenbuterol.

Core-Shell Molecularly Imprinted Polymer Nanocomposites for Biomedical and Environmental Applications

Core-shell polymers represent a class of composite particles comprising of minimum two dissimilar constituents, one at the center known as a core which is occupied by the other called shell. Core-shell molecularly imprinting polymers (CSMIPs) are composites prepared via printing a template molecule (analyte) in the coreshell assembly followed by their elimination to provide the everlasting cavities specific to the template molecules. Various other types of CSMIPs with a partial shell, hollow-core and empty-shell are also prepared. Numerous methods have been reported for synthesizing the CSMIPs. CSMIPs composites could develop the ability to identify template molecules, increase the relative adsorption selectivity and offer higher adsorption capacity. Keen features are measured that permits these polymers to be utilized in numerous applications. It has been developed as a modern technique with the probability for an extensive range of uses in selective adsorption, biomedical fields, food processing, environmental applications, in utilizing the plant's extracts for further applications, and sensors. This review covers the approaches of developing the CSMIPs synthetic schemes, and their application with special emphasis on uses in the biomedical field, food care subjects, plant extracts analysis and in environmental studies.

Polymethacryloyl-L-Phenylalanine [PMAPA]-Based Monolithic Column for Capillary Electrochromatography

The ability to detect catecholamines (CAs) and their metabolites is vital to understand the mechanism behind the neuronal diseases. Neurochemistry aims to provide an improved pharmacological, molecular and physiological understanding of complex brain chemistries by analytical techniques. Capillary electrophoresis (CE) is one such analytical technique that enables the study of various chemical species ranging from amino acids and peptides to natural products and drugs. CE can easily adapt the changes in research focus and in recent years remains an applicable technique for investigating neuroscience and single cell neurobiology. The prepared phenylalanine-based hydrophobic monolithic column, Polymethacryloyl-L-phenylalanine [PMAPA], was used as a stationary phase in capillary electrochromatography to separate CAs that are similar in size and shape to each other including dopamine (DA) and norepinephrine (NE) via hydrophobic interactions. Separation carried out in a short period of 17 min was performed with the electrophoretic mobility of 5.54 × 10−6 m2 V−1 s−1 and 7.60 × 10−6 m2 V−1 s−1 for DA and NE, respectively, at pH 7.0, 65% acetonitrile ratio with 100 mbar applied pressure by the developed hydrophobic monolithic column without needing any extra process such as imprinting or spacer arms to immobilize ligands used in separation.

Molecularly Imprinted Polymer Based Sensors for Medical Applications

Sensors have been extensively used owing to multiple advantages, including exceptional sensing performance, user-friendly operation, fast response, high sensitivity and specificity, portability, and real-time analysis. In recent years, efforts in sensor realm have expanded promptly, and it has already presented a broad range of applications in the fields of medical, pharmaceutical and environmental applications, food safety, and homeland security. In particular, molecularly imprinted polymer based sensors have created a fascinating horizon for surface modification techniques by forming specific recognition cavities for template molecules in the polymeric matrix. This method ensures a broad range of versatility to imprint a variety of biomolecules with different size, three dimensional structure, physical and chemical features. In contrast to complex and time-consuming laboratory surface modification methods, molecular imprinting offers a rapid, sensitive, inexpensive, easy-to-use, and highly selective approaches for sensing, and especially for the applications of diagnosis, screening, and theranostics. Due to its physical and chemical robustness, high stability, low-cost, and reusability features, molecularly imprinted polymer based sensors have become very attractive modalities for such applications with a sensitivity of minute structural changes in the structure of biomolecules. This review aims at discussing the principle of molecular imprinting method, the integration of molecularly imprinted polymers with sensing tools, the recent advances and strategies in molecular imprinting methodologies, their applications in medical, and future outlook on this concept.

Sensitive and Facile Electrochemiluminescent Immunoassay for Detecting Genetically Modified Rapeseed Based on Novel Carbon Nanoparticles

A highly sensitive electrochemiluminescent (ECL) immunoassay targeting PAT/ bar protein was facilely developed for genetically modified (GM) rapeseed detection using carbon nanoparticles (CNPs) originally prepared from printer toner. In this work, CNPs linked with antibody for PAT/ bar protein were used to modify a working electrode. After an immunoreaction between the PAT/ bar protein and its antibody, the immunocomplex formed on the electrode receptor region resulted in an inhibition of electron transfer between the electrode surface and the ECL substance, thus led to a decrease of ECL response. Under the optimal conditions, the ECL responses linearly decreased as the increase of the PAT/ bar protein concentration and the GM rapeseed RF3 content in the ranges of 0.10-10 ng/mL and 0.050-1.0%, with the limits of detection of 0.050 ng/mL and 0.020% (S/N = 3). These results open a facile, sensitive, and rapid approach for the safety control of agricultural GM rape.