Enzyme-free colorimetric sensor based on molecularly imprinted polymer and ninhydrin for methamphetamine detection.

Digital image colorimetry was applied to introduce a rapid, portable, and non-enzymatic test for methamphetamine measurements in urine. Imprinted polymer was synthesized in a simple, low-cost process and utilized for selective extraction of analyte from the sample in combination with the well-known ninhydrin color test. Applying the digital camera on a mobile phone, RGB basic color data were obtained, and calibration curves were developed for different concentrations of methamphetamine. Optimization of the test condition was carried out by changing some effective parameters such as extraction time and pH. The results were compared with some similar structural compounds indicating great potential for use as a selective and semi-quantitative field test for this drug. An acceptable linear range (5-100 µM) and detection limit (1.44 µM) as well as good agreement with the reference method, makes this fast portable method, an easy and reliable test for the analysis of methamphetamine in biological samples.

Selective and ultrasensitive citric acid assay in urine samples using a MWCNT/Fe3O4 nanoparticle-modified carbon paste electrode.

A carbon paste electrode (CPE) modified with multiwalled carbon nanotubes and magnetite nanoparticles is introduced (CNT/Fe3O4-CPE) as the most sensitive citric acid (CA) electrochemical sensor reported so far. The structural and spectroscopic characterization by Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy is presented. The electrocatalytic performance of the electrode was substantiated using cyclic voltammetry and electrochemical impedance spectroscopy (EIS). Performing voltammetric experiments at different pH values and various scan rates gave some evidence for the electro-oxidation mechanism of CA. The EIS study gave an obvious indication for the enhancement of the charge transfer rate of CA by the nanocomposite. Various parameters affecting the electrode performance were studied. Using differential pulse voltammetry it was found that the CNT/Fe3O4-CPE showed a linear dynamic range of 5.0 × 10-7-1 × 10-4 mol L-1, an excellent sensitivity of 5184 µA mM-1 cm-2, and a detection limit of 3.6 × 10-7 mol L-1 for CA determination. The relative standard deviation was found to be 3.1% (n = 3). The method was utilized for CA determination in urine samples without utilizing complicated sample pretreatment.

An ultra-sensitive and highly selective impedimetric sensor for vitamin D measurement based on a novel imprinted polymer synthesized utilizing template-derived functional monomer.

A novel vitamin D3-imprinted (VD)-polymer was synthesized utilizing a functional monomer derived from vitamin D3. Acryloyl chloride reacted with VD leading to a functional monomer capable of interaction with VD during the molecularly imprinted polymer (MIP) synthesis step. Vitamin D3-derived functional monomer and divinylbenzene were copolymerized in the presence of vitamin D3 in order to create a new MIP, holding VD selective cavities, after template (VD) removal from the polymer. The MIP nanoparticles were used for the modification of a carbon paste electrode to fabricate VD selective sensor. The charge transfer resistance of Fe(CN)63-/Fe(CN)64-couple for the MIP-modified electrode increased significantly in the presence of VD; whereas, the non-imprinted polymer (NIP)-CPE electrode was not affected by VD, suggesting well acting of recognition sites of the MIP nanoparticles, incorporated into the electrode. The sensing mechanism was attributed to a gate effect principle. Interring of VD molecules to the selective sites of the MIP nanoparticles, existing on the electrode surface, makes the MIP particles swell and this leads to blocking the majority of routes via which the probe electroactive species accesses the carbon particles at the electrode surface. The MIP electrode was not sensitive to some molecules structurally similar to VD, suggesting a highly selective nature of the designed sensor. The new VD sensor impedimetric response as a function of the logarithm of VD concentration was found to be linear in the range of 1.0-100.0 pM. The detection limit of the sensor was estimated to be 0.22 pM. The sensor was used for VD level estimation in plasma samples.

A novel chloride selective potentiometric sensor based on graphitic carbon nitride/silver chloride (g-C3N4/AgCl) composite as the sensing element.

In this research, AgCl anchored graphitic carbon nitride (g-C3N4) was introduced as a novel potentiometric sensing element. A g-C3N4/AgCl-modified carbon paste electrode (CPE) was fabricated and used as an outstandingly selective potentiometric sensor to determine Cl- in water samples. The g-C3N4/AgCl nanocomposite was characterized with SEM, XRD and FT-IR techniques. It was demonstrated that, the incorporation of 5% of g-C3N4/AgCl, as a chloride ionophore in a CPE, results in a stable potential response of the electrode to chloride ion. The Nernstian slope of the electrode response was 55.4 (±0.3) mVdecade-1, over a wide linear concentration range of 1 × 10-6-1 × 10-1 mol L-1 and the detection limit of the electrode was estimated to be 4.0 × 10-7 mol L-1. The g-C3N4/AgCl-modified CPE electrode provided fast response time and long-term stability (more than 2 months) while the potential interfering ions such as I-, Br-, and CN- showed no significant effect on the potential response. Since these interfering ions affected the response of the CPE electrode, modified with AgCl, highlighting the interesting effect of g-C3N4 on the sensor performance. This innovative electrode was shown to be a sensitive and accurate sensor for chloride ion content estimation in water samples.

Highly selective extraction and voltammetric determination of the opioid drug buprenorphine via a carbon paste electrode impregnated with nano-sized molecularly imprinted polymer.

An electrochemical sensor for the opioid drug buprenorphine (BUP) is described. Molecularly imprinted polymer nanoparticles (nanoMIP) were prepared and used to modify a carbon paste electrode (CPE). The BUP-imprinted polymer was synthesized using precipitation polymerization. The resulting polymer along with multiwalled carbon nanotubes (MWCNT) was used to fabricate the modified CPE which exhibited an anodic peak at about +0.73 V (vs. Ag/AgCl) for BUP. The MIP on the CPE functions as selective recognition element with an imprinting factor of 5.6. The assay consists of two-steps, viz. analyte extraction at the electrode surface and differential pulse voltammetric determination of BUP. The effects of various parameters on the electrochemical signal were optimized, and the selectivity of the modified CPE over cross reactants was studied. At optimum experimental conditions, the response is linear in the 1 nM to 50 µM BUP concentration range, and the detection limit is 0.6 nM (at S/N = 3). This method was applied to the determination of BUP in spiked urine with acceptable relative standard deviations (3.2-4.4%). Graphical abstract Schematic representation of buprenorphine (BUP) recognition and voltammetric determination at the surface of carbon paste electrode modified with imprinted polymer and carbon nanotubes.

Ultra-trace detection of methamphetamine in biological samples using FFT-square wave voltammetry and nano-sized imprinted polymer/MWCNTs -modified electrode.

An efficient voltammetric method for trace level monitoring of methamphetamine (MTM) stimulant drug in the human urine and serum samples is established. This method is based on fast fourier transform square wave voltammetric (FFT-SWV) determination of MTM at a molecularly imprinted polymer (MIP)/multi-walled carbon nanotube (MWCNTs)-modified carbon paste electrode. Voltammetric techniques development for electrochemical assay of MTM is a challenge, due to the weak electroactivity of this drug. Herein, MTM-imprinted nanopolymer was synthesized, using a simple precipitation polymerization method. The resulting polymer, along with MWCNT was then used to fabricate the modified carbon paste electrode which showed a well-defined anodic peak for MTM at about +1.0 V(vs. Ag/AgCl); whereas, the related blank electrode exhibited considerably lower signal at the same conditions. Utilizing the highly efficient MIP, MWCNTs (which increased the charge transfer phenomenon at the electrode surface) and the advanced electrochemical technique of FFT-SWV (which increased the created signal intensity) caused this method to be a high sensitive and selective approach for MTM measurement. In the optimum experimental conditions, the proposed sensor, exhibited linear response range of 1.0 × 10-8 -1.0 × 10-4 mol L-1 and the detection limit of 8.3 × 10-10 mol L-1 with acceptable relative standard deviations (RSD%) for real samples (1.0-3.5%). Herein, the first MIP-based voltammetric sensor for MTM which also exhibits the lowest detection limit, ever reported, is introduced. This approach seems to provide an effective way for rapid screening of MTM in human urine and serum samples.

A new carbon paste electrode modified with MWCNTs and nano-structured molecularly imprinted polymer for ultratrace determination of trimipramine: The crucial effect of electrode components mixing on its performance.

A novel carbon nanocomposite paste electrode was prepared and used as a voltammetric sensor for ultratrace determination of trimipramine (TRI) which currently used for the treatment of psychiatric disorders. For this aim, nanoparticles of molecularly imprinted polymer (MIP), synthesized by precipitation polymerization method, and multi-walled carbon nanotubes (MWCNTs) were embedded in a nanocomposite paste electrode. The nanocomposite mixing style demonstrated a significant influence on the final electrode performance. The sensor exhibited linear response range of 1.0 × 10-10-2.5 × 10-8 mol L-1 and very high sensitivity of 2131 µA µâ€¯mol L-1. The lower detection limit of the sensor was calculated to be 4.5 × 10-11 mol L-1 (S/N = 3). This sensor was applied successfully for highly selective determination of TRI in pharmaceutical formulations, urine and serum samples without applying any sample pretreatment.

An innovative method for synthesis of imprinted polymer nanomaterial holding thiamine (vitamin B1) selective sites and its application for thiamine determination in food samples.

Thiamine is a highly hydrophilic vitamin which is insoluble in common organic solvents, utilized traditionally for synthesis of molecularly imprinted polymer. In this work a simple strategy is introduced to overcome the insolubility problem of thiamine and prepare an efficient MIP in chloroform. Thiamine, as a cationic agent, involved in an ion-pair complex with anionic species of trimethylsilyl-propane sulfonate (TPS). The ion-pair was then transferred effectively to apolar solvent of chloroform where the polymerization reaction was conducted to produce nano-sized thiamine imprinted polymer. The experimental conditions such as pH, ionic strength and carrier agent/thiamine mole ratio were optimized to maximize the thiamine amount, transported to chloroform. The characteristics of the polymer were investigated by FT-IR, SEM and Zeta potential analysis techniques. The experimental adsorption isotherms of thiamine onto MIP and non-imprinted polymer (NIP) were determined and well fitted by Langmuir-Freundlich model. Maximum binding capacities of the MIP and NIP materials were obtained as 106.1 and 35.7 µmol g-1, respectively. After investigation and fixing of the experimental conditions on thiamine extraction by the MIP, it was successfully utilized for thiamine extraction from food samples and its determination by fluorimetric method.

Synthesis of nano-sized timolol-imprinted polymer via ultrasonication assisted suspension polymerization in silicon oil and its use for the fabrication of timolol voltammetric sensor.

A novel timolol voltammetric sensor based on the nano-sized molecularly imprinted polymer (nano-MIP)-modified carbon paste electrode was introduced. Timolol-imprinted polymers (MIP) were synthesized by the ultrasonic assisted suspension polymerization in silicon oil. The MIP nanoparticles were then embedded in a carbon paste (CP) electrode in order to prepare the nano-MIP-CP electrode. Timolol was extracted in the electrode for a definite time and then it was analyzed by square wave voltammetry, found to be an effective determination method. The electrode showed higher response to timolol, compared to the CP electrode, and CP electrode modified with non-imprinted polymer (nano-NIP-CP). Various factors, known to affect the response behavior of the nano-MIP-CP electrode, were investigated and optimized. The sensor exhibited distinct linear response ranges of 1.0×10-7-2.1×10-6M with the sensitivity of 71.523µAµM-1. The lower detection limit of the sensor was calculated to be 2.3×10-8M (S/N=3). The sensor was applied successfully for timolol determination in pharmaceutical formulations, blood serum and urine samples.

Ultratrace Detection of Histamine Using a Molecularly-Imprinted Polymer-Based Voltammetric Sensor.

Rapid and cost-effective analysis of histamine, in food, environmental, and diagnostics research has been of interest recently. However, for certain applications, the already-existing biological receptor-based sensing methods have usage limits in terms of stability and costs. As a result, robust and cost-effective imprinted polymeric receptors can be the best alternative. In the present work, molecularly-imprinted polymers (MIPs) for histamine were synthesized using methacrylic acid in chloroform and acetonitrile as two different porogens. The binding affinity of the MIPs with histamine was evaluated in aqueous media. MIPs synthesized in chloroform displayed better imprinting properties for histamine. We demonstrate here histamine MIPs incorporated into a carbon paste (CP) electrode as a MIP-CP electrode sensor platforms for detection of histamine. This simple sensor format allows accurate determination of histamine in the sub-nanomolar range using an electrochemical method. The sensor exhibited two distinct linear response ranges of 1 × 10-10-7 × 10-9 M and 7 × 10-9-4 × 10-7 M. The detection limit of the sensor was calculated equal to 7.4 × 10-11 M. The specificity of the proposed electrode for histamine is demonstrated by using the analogous molecules and other neurotransmitters such as serotonin, dopamine, etc. The MIP sensor was investigated with success on spiked serum samples. The easy preparation, simple procedure, and low production cost make the MIP sensor attractive for selective and sensitive detection of analytes, even in less-equipped laboratories with minimal training.