Novel synthesis of a dual fluorimetric sensor for the simultaneous analysis of levodopa and pyridoxine.

Herein, a fluorimetric sensor was fabricated based on molecularly imprinted polymers (MIPs) with two types of carbon dots as fluorophores. The MIPs produced had similar excitation wavelengths (400 nm) and different emission wavelengths (445 and 545 nm). They were used for the simultaneous analysis of levodopa and pyridoxine. First, two types of carbon dots, i.e. nitrogen-doped carbon dots (NCDs) with a quantum yield of 43%, and carbon dots from o-phenylenediamine (O-CDs) with a quantum yield of 17%, were prepared using the hydrothermal method. Their surfaces were then covered with MIPs through the reverse microemulsion method. Finally, a mixture of powdered NCD@MIP and O-CD@MIP nanocomposites was used for the simultaneous fluorescence measurement of levodopa and pyridoxine. Under optimal conditions using response surface methodology and Design-Expert software, a linear dynamic range of 38 to 369 nM and 53 to 457 nM, and detection limits of 13 nM and 25 nM were obtained for levodopa and pyridoxine, respectively. The capability of the proposed fluorimetric sensor was investigated in human blood serum and urine samples. Graphical Abstract Schematic representation of nitrogen-doped carbon dots (NCDs), carbon dots from o-phenylenediamine (O-CDs), NCDs coated with imprinted polymers (NCD@MIPs), and O-CDs coated with imprinted polymers (O-CD@MIPs) in the presence and absence of levodopa and pyridoxine.

Ultra-sensitive and selective electrochemical biosensor with aptamer recognition surface based on polymer quantum dots and C60/MWCNTs- polyethylenimine nanocomposites for analysis of thrombin protein.

In this study, an ultra-sensitive and selective Thrombin biosensor with aptamer-recognition surface is introduced based on carbon nanocomposite. To prepare the this biosensor, screen-printed carbon electrodes (SPCE) were modified with a nanocomposite made from fullerene (C60), multi-walled carbon nanotubes (MWCNTs), polyethylenimine (PEI) and polymer quantum dots (PQdot). The unique characteristics of each component of the C60/MWCNTs-PEI/PQdot nanocomposite allow for synergy between nanoparticles while polymer quantum dots resulted in characteristics such as high stability, high surface to volume ratio, high electrical conductivity, high biocompatibility, and high mechanical and chemical stability. The large number of amine groups in C60/MWCNTs-PEI/PQdot nanocomposite created more sites for better covalent immobilization of amino-linked aptamer (APT) which improved the sensitivity and stability of the aptasensor. Differential Pulse Voltammetry (DPV) method with probe solution was used as the measurment method. Binding of thrombin protein to aptamers immobilized on the transducer resulted in reduced electron transfer at the electrode/electrolyte interface which reduces the peak current (IP) in DPV. The calibration curve was drawn using the changes in the peak current (ΔIP),. The proposed aptasensor has a very low detection limit of 6 fmol L-1, and a large linear range of 50 fmol L-1 to 20 nmol L-1. Furthermore, the proposed C60/MWCNTs-PEI/PQdot/APT aptasensor has good reproducibility, great selectivity, low response time and a good stability during its storage. Finally, the application of the proposed aptasensor for measuring thrombin on human blood serum samples was investigated. This aptasensor can be useful in bioengineering and biomedicine applications as well as for clinical studies.

Preparation and comparison of molecularly imprinted polymer fluorimetric nanoprobe based on polymer dots and carbon quantum dots for determination of acetamiprid using response surface method.

In this study molecularly imprinted polymers (MIP) based on carbon quantum dots (CQDs) and polymer dots (PDs) are developed for selective determination of acetamiprid using fluorometry. The measurement is based on the fluorescence quenching of CQDs and PDs in the presence of acetamiprid. PDs were prepared using a one-step aqueous synthesis method from ascorbic acid and diethylenetriamine at room temperature. CQDs were prepared from the same materials using the hydrothermal method at 180 °C. These particles were characterized using field emission scanning electron microscopy (FE-SEM), FTIR, dynamic light scattering (DLS), X-ray diffraction (XRD), UV-Vis, and fluorescence. The quantum yield was 47% for PDs and 8% for CQDs. Then, molecularly imprinted polymers (MIP) were prepared based on PDs and CQDs using reverse microemulsion method. The fluorescence quenching of CQD@MIPs and PD@MIPs was investigated at an excitation wavelength of 350 nm and emission wavelength of 440 nm in the presence of a template. Other variables affecting the fluorescence peaking were optimized using design expert software. The results illustrate that the use of PD@MIPs had a wide dynamic range 0.08-109 nmol L-1, good accuracy and detection limit of 0.02 nmol L-1, while using CQD@MIPs led to a lower dynamic range 0.36-64 nmol L-1, and detection limit of only 0.11 nmol L-1. The responses of the optical nanoprobe for acetamiprid in water (recovery 92-102%) and apple (recovery 92-103%) were also investigated. Graphical abstract Schematic representation of preparation polymer dots (PDs), carbon quantum dots (CQDs), PDs coated with imprinted polymers (PD@MIPs), and CQDs coated with imprinted polymers (CQD@MIPs) in the presence and absence of acetamiprid.

Manufacturing of a Sensitive and Selective Optical Sensor Based on Molecularly Imprinted Polymers and Green Carbon Dots Synthesized from Cedrus Plant for Trace Analysis of Propranolol.

In this article, a new optical sensor was developed using a molecularly imprinted polymers layer coated with new green carbon dots (CDs) for the determination of propranolol. First, the CDs were synthesized for the first time from Cedrus plant through the hydrothermal method. Then, a nanolayer molecularly imprinted polymer (MIP) was applied on the CDs (MIP-CDs) in the presence of propranolol as a template using a reverse microemulsion technique. Afterward, propranolol was removed from MIP-CDs nanocomposites using a mixture of ethanol and acetonitrile, and the obtained nanocomposite was used as a fluorescence sensor for propranolol determination. Under the optimal conditions, the sensor response was linear in the range of 0.8 - 65.0 nmol L-1 with a detection limit of 0.2 nmol L-1. The results confirmed that the sensor has some advantages such as cost-effectiveness, rapid response, high sensitivity and selectivity for propranolol determination.

An ultrasensitive electrochemical anti-lysozyme aptasensor with biorecognition surface based on aptamer/amino-rGO/ionic liquid/amino-mesosilica nanoparticles.

In this work, a novel method based on aptamers is proposed for electrochemical measurement of lysozyme. To this end, screen-printed carbon electrode (SPCE) was modified with a nanocomposite made from amino-reduced graphene oxide (Amino-rGO) synthesized from natural graphite powder, an ionic liquid (IL), and amino-mesosilica nanoparticles (Amino-MSNs). The composition of the nanocomposite (Amino-rGO/IL/Amino-MSNs) results in high thermal and chemical stability, conductivity, surface-to-volume ratio, cost efficiency, biocompatibility, and great bioelectrocatalysis characteristics. Presence of numerous amino groups, as well as remaining oxygen defects in rGO, provides a suitable site for immobilization of aptamers. Furthermore, use of this nanocomposite leads to considerable enhancement of the electrochemical signal and improved method sensitivity. Covalent coupling of aptamer's amino groups with that of the nanocomposite using glutaraldehyde (GLA) as a linker helps immobilize amino-linked lysozyme aptamers (Anti-Lys aptamers) on nanocomposite. The modified electrode was characterized using electrochemical methods such as cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). The immobilized aptamer selectively adsorbs lysozyme (Lys) on the electrode interface, leading to increased Charge Transfer Resistance (RCT) in EIS and decrease in the DPV peak currents which are used as analytical signals. Two separate calibration curves were drawn using the data acquired from EIS and DPV. The prepared anti-Lys aptasensor has two very low LODs equal to 2.1 and 4.2 fmol L-1 with wide detection ranges of 10 fmol L-1 to 200 nmol L-1, and 20 fmol L-1 to 50 nmol L-1 for EIS and DPV calibration curves, respectively. The SPCE/Amino-rGO/IL/Amino-MSNs/APT also showed high reproducibility, specificity, sensitivity, and rapid response to Lys which has various applications in fields of bioengineering and biomedicine.

Application of coated green source carbon dots with silica molecularly imprinted polymers as a fluorescence probe for selective and sensitive determination of phenobarbital.

Herein, a selective and sensitive fluorescence sensor was developed for the detection of phenobarbital, an epilepsy drug, using molecularly imprinted polymers (MIPs) coated on the surface of green source carbon dots (GSCDs). First, GSCDs were synthesized through a hydrothermal method using Cedrus as a carbon source. Then, a MIPs-GSCDs as a fluorescence probe was obtained by coating a thin film of silica on the surface of the GSCDs using a reverse micro emulsion method. In this step, phenobarbital, 3-aminopropyltriethoxysilane (APTES) and tetraethoxysilane (TEOS) were applied as a template, a functional monomer, and cross linker, respectively. The fluorescence signal of MIPs-GSCDs was selectively quenched by phenobarbital rebinding with MIP cavities. The fluorescence quenching signal was applied for phenobarbital sensing at the pH = 8 without the interference of other materials. After optimizing the factors affecting the sensor's response, a linear range between 0.4 and 34.5 nmol L-1 with a detection limit of 0.1 nmol L-1 was obtained. The sensor's capability in the real sample analysis was investigated by phenobarbital determination in a human blood plasma samples.

An ultrasensitive and selective electrochemical aptasensor based on rGO-MWCNTs/Chitosan/carbon quantum dot for the detection of lysozyme.

An aptamer-based method is described for the electrochemical determination of lysozyme. A glassy carbon electrode was modified with a nanocomposite composed of reduced graphene oxide (rGO), multi-walled carbon nanotubes (MWCNTs), chitosan (CS), and a synthesized carbon quantum dot (CQD) from CS. The composition of the nanocomposite (rGO-MWCNT/CS/CQD) warrants a high surface-to-volume ratio, high conductivity, high stability, and great electrocatalytic activity. This nanocomposite provides a suitable site for better immobilization of aptamers due to the existence of many amino and carboxyl functional groups, and remaining oxygen-related defects properties in rGO. In addition, this nanocomposite allows considerable enhancement of the electrochemical signal and contributes to improving sensitivity. The amino-linked lysozyme aptamers were immobilized on the nanocomposite through covalent coupling between the amino groups of the aptamer and the amino groups of the nanocomposite using glutaraldehyde (GLA) linker. The modified electrode was characterized by electrochemical methods including differential pulse voltammetry (DPV), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). In the presence of lysozyme, the immobilized aptamer selectively caught the target lysozyme on the electrode interface that leads to a decrease in the DPV peak current and an increase in Charge Transfer Resistance (Rct) in EIS as an analytical signal. Using the obtained data from DPV and EIS techniques, two calibration curves were drawn. The anti-lysozyme aptasensor proposed has two very low LODs. These measures are 3.7 and 1.9 fmol L-1 within the wide detection ranges of 20 fmol L-1 to 10 nmol L-1, and 10 fmol L-1 to 100 nmol L-1 for DPV and EIS calibration curves, respectively. The GCE/rGO-MWCNT/CS/CQD showed sensitivity, high reproducibility, specificity and rapid response for lysozyme which can be used in biomedical fields.

Lysozyme aptasensor based on a glassy carbon electrode modified with a nanocomposite consisting of multi-walled carbon nanotubes, poly(diallyl dimethyl ammonium chloride) and carbon quantum dots.

An aptamer-based method is described for electrochemical determination of lysozyme. A glassy carbon electrode was modified with a nanocomposite composed of multi-walled carbon nanotubes, poly(diallyl dimethyl ammonium chloride), and carbon quantum dots. The composition of the nanocomposite (MWCNT/PDDA/CQD) warrants good electrical conductivity and a high surface-to-volume ratio. The lysozyme-binding aptamers were immobilized on the nanocomposite via covalent coupling between the amino groups of the aptamer and the carboxy groups of the nanocomposite. The modified electrode was characterized by electrochemical impedance spectroscopy, cyclic voltammetry and differential pulse voltammetry. The use of this nanocomposite results in a considerable enhancement of the electrochemical signal and contributes to improving sensitivity. Hexacyanoferrate was used as an electrochemical probe to study the dependence of the peak current on lysozyme concentration. In the presence of lysozyme, the interaction of lysozyme with immobilized aptamer results in a decrease of the peak current, best measured at +0.15 V vs. Ag/AgCl. A plot of peak current changes versus the logarithm of the lysozyme concentration is linear in the 50 fmol L-1 to 10 nmol L-1 concentration range, with a 12.9 fmol L-1 detection limit (at an S/N ratio of 3). The method is highly reproducible, specific and sensitive, and the electrode has a rapid response. It was applied to the determination of lysozyme in egg white, serum, and urine. Graphical abstract Schematic of a nanocomposite composed of multi-walled carbon nanotubes (MWCNTs), poly(diallyldimethyl ammonium chloride) (PDDA), and carbon quantum dots (CQDs) for use in a lysozyme aptasensor. The aptamer was immobilized on the surface, and bovine serum albumin (BSA) was applied to block the surface. The changes of peak current for the electrochemical probe hexacyanoferrate (Fe(CN)63-/4-) in the presence and absence of lysozyme was traced.

Electrochemical study of quinone redox cycling: A novel application of DNA-based biosensors for monitoring biochemical reactions.

This paper presents the results of an experimental investigation of voltammetric and impedimetric DNA-based biosensors for monitoring biological and chemical redox cycling reactions involving free radical intermediates. The concept is based on associating the amounts of radicals generated with the electrochemical signals produced, using differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). For this purpose, a pencil graphite electrode (PGE) modified with multiwall carbon nanotubes and poly-diallydimethlammonium chloride decorated with double stranded fish sperm DNA was prepared to detect DNA damage induced by the radicals generated from a redox cycling quinone (i.e., menadione (MD; 2-methyl-1,4-naphthoquinone)). Menadione was employed as a model compound to study the redox cycling of quinones. A direct relationship was found between free radical production and DNA damage. The relationship between MD-induced DNA damage and free radical generation was investigated in an attempt to identify the possible mechanism(s) involved in the action of MD. Results showed that DPV and EIS were appropriate, simple and inexpensive techniques for the quantitative and qualitative comparisons of different reducing reagents. These techniques may be recommended for monitoring DNA damages and investigating the mechanisms involved in the production of redox cycling compounds.