Super-High-Resolution Densitometry by Optical Trapping of a Single-Molecularly Imprinted Polymer Particle for Subsingle Molecule Detection.

In this study, for the first time, we have shown that the single nano-/microparticle trapping ability of optical tweezers combined with the high selectivity of molecularly imprinted polymers (MIPs) provides an indispensable molecular-level instrument for chemical sciences. Trapping a single MIP inside a solution and analyzing its Brownian motion allow for real-time determination of its target molecule [trimipramine (TMP) in our case] content. This method is also utilized to precisely measure TMP concentration in the bulk solution. The detection and optical volumes, respectively, defined as single MIP volume and laser focal volume, were about a few femtoliters. According to our data within a detection volume inside the bulk solution, 0.02-0.25 target molecules could be detectable with a detection limit of 0.005 molecules. Thus, we detected 1/1000th of the subsingle molecule in detection volume by high-resolution densitometry.

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.

Molecularly imprinted polymer specific to creatinine complex with copper(II) ions for voltammetric determination of creatinine.

Synthesis of creatinine-imprinted polymer is challenging because of its insolubility in aprotic solvents, traditionally utilized for synthesizing molecularly imprinted polymer (MIP). Moreover, creatinine is not electroactive at conventional electrodes, and thus, introducing an electrochemical sensing platform for its determination is a difficult target. This study addressed the above-cited issues to introduce a novel creatinine voltammetric sensor with high selectivity and sensitivity. Creatinine-copper complex was found to be soluble in acetonitrile and was utilized as a template for the MIP synthesis. Methacrylic acid, ethylene glycol dimethacrylate, and azobisisobutyronitrile were used as functional monomers, cross-linker, and initiator, respectively. The MIP holding creatinine sites were used to modify the carbon paste electrode. Since creatinine did not exhibit a significant voltammetric signal, an indirect sensing technique was employed. This was based on using Cu(II) ion as an electrochemical probe. The MIP-modified electrode signal for copper ion was significantly improved in the presence of creatinine. However, the introduction of creatinine in the Cu(II) solution did not affect the NIP-modified electrode response to copper ion. The proposed sensor indicated a linear current response in the range 1 × 10-7-1 × 10-5 mol L-1 with a detection limit of 5.9 × 10-8 mol L-1 (S/N = 3). Moreover, this method presents excellent performance in real sample analysis, with values of favorable creatinine recovery in plasma. The system exhibits acceptable precision (RSD = 4.04) and favorable selectivity toward creatinine.

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.

Ultra selective and high-capacity dummy template molecular imprinted polymer to control quorum sensing and biofilm formation of Pseudomonas aeruginosa.

Here a highly selective molecular imprinting polymer was developed to attenuate biofilm formation of the multidrug-resistant pathogen Pseudomonas aeruginosa by disrupting the intermolecular signaling system. Firstly, a dummy template molecular imprinting polymer (MIP) was rationally designed through molecular modeling to capture 2-heptyl-3-hydroxy-4-quinolone (Pseudomonas quinolone signal). This multifunctional signaling molecule interferes with the pathogenicity of P. aeruginosa as an auto-inducer. Then, the synthesized MIP and the non-imprinted polymer (NIP) as reference polymer were evaluated for their binding capacity and biofilm inhibition. The results indicated a significant difference in biofilm inhibition (∼56%) between imprinted (∼67%) and non-imprinted (∼11%) polymer, which is an impressive level, especially for the treatment of various surfaces affected by P. aeruginosa. These results open a new window in the special biological application of MIPs as a promising candidate to reduce concerns in clinical or industrial issues by preventing microbial infections.

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.

A novel non-enzymatic sensor for prostate cancer biomarker sensing based on electrocatalytic oxidation of sarcosine at nanostructured NiMn2O4 impregnated carbon paste electrode.

This work addresses the electrocatalytic activity of a binary metal oxide catalyst of NiMn2O4 for electroxidation of sarcosine, the well-known prostate cancer biomarker. The nanocatalyst described was prepared via hydrothermal synthesis route, followed by calcination at 800 °C. Field emission scanning electron microscopy and X-ray diffraction were applied to obtain information about the material morphology and structure. A carbon paste electrode modified with nano-NiMn2O4 showed unique catalytic activity in sarcosine electroxidation which led to a significant rise in oxidation current (about four times) in comparison with the blank electrode. However, the carbon paste electrodes containing single oxides of NiO and Mn2O3 exhibited no considerable enhancement in sarcosine signal. The cyclic voltammetry results indicated that the Mn3+/Mn4+ couple was responsible for sarcosine oxidation, and NiO may enhance the content of Mn4+species in NiMn2O4 material. The carbon paste-based NiMn2O4 electrode was applied in the sensitive determination of sarcosine in the concentration range of 0.01-5.0 µM with the relative standard deviation of 3.49% (n = 5). The detection limit and quantification limit of the probe were determined to be 3.8 and 12 nM, respectively. The remarkable sensitivity and high selectivity of the method approved the sensor applicability in measurement of sarcosine content in urine samples.

Y-shape structured azo dyes with self-transforming feature to zwitterionic form as sensitizer for DSSC and DFT investigation of their photophysical and charge transfer properties.

Two novel azo dyes with D-π-A-π-D structures were designed and synthesized to investigate the relationship between molecular structure and sensitizing performance on applying for dye-sensitized solar cells (DSSCs) in comparison with their linear counterparts. Introducing hydroxyl auxiliary groups and arranging π-conjugation length as two parallel and series structural architectures, Y-shape and linear, led to red shift in absorption wavelength and increase in absorption intensity for the Y-shape pattern providing an efficient charge transfer pathway and improved Jsc and η of the DSSCs. Emerging a zwitterionic form, azonium structure, of the sensitizer in parallel configuration for the dyes 1a.p and 1b.p, enhanced light absorption domain and changed anchoring fashion could engendering improved electronic overlapping. The easily-synthesized dyes were evaluated for photophysical and electrochemical properties and turned out that the parallel-decorated dyes displayed better results than the series types as photosensitizers for DSSCs. ATR and Raman spectra clearly showed the adsorption of these dyes on the TiO2 surface. Operational tests of DSSCs, coated by titled azo dyes, illustrated that decorating π-conjugation pattern as parallel structure as well as accessorizing the donor unit with hydroxyl groups improved the photovoltaic performance. Optimized band gap due to participating the azonium structure and restricted electron recombination as well as rectified dye regeneration were proposed as main elements in enhancing performance parameters. A higher solar conversion efficiency was recorded for DSSCs based on the Y-shape dyes compared to other meta azo dye-based cells that were previously reported. Computational calculations were used to corroborate the opto-electrochemical traits of the dyes with a special concern on the influence of structural pattern on photovoltaic features.

Improving the optoelectronic efficiency of novel meta-azo dye-sensitized TiO2 semiconductor for DSSCs.

A series of novel azo dyes possessing varying conjugation lengths and different donor moieties, based on 5-amino isophthalic acid were designed and synthesized. Azobenzene unites were utilized as the π-spacer part to extend the conjugation range and connect the donor to acceptor unit. When the dialkylamino substituent was changed from dimethyl to diethanol, a red shift in the absorption spectra and λonset was observed. The photophysical and electrochemical properties of the straightforward-synthesized dyes were investigated in solution and on photoanode surface which promised the suitability of the dyes as photosensitizers for dye sensitized solar cells (DSSCs). Increased dye adsorption strength on the TiO2 surface as well as light harvesting capability was expected due to bearing two anchoring-electron accepting groups which could lead to enhanced electron transfer (ET). The ATR absorption spectra clearly showed that these dyes were adsorbed on the TiO2 surface. It was realized that increasing π-conjugation length as well as hydroxyl containing donor group gave rise to improved photovoltaic performance of DSSCs. Reduced band gap along with suppressed electron recombination and amended dye regeneration were recognized to play an important role in enhancing performance parameters. DSSCs based on these dyes exhibited higher solar conversion efficiency in comparison with efficiency of other meta azo dyes that were previously synthesized. Theoretical calculations (DFT/TDDFT) expressed that among the dyes, members 3a and 3b possessed localized and non-continuous electron distribution in their frontier orbitals as well as maximum amount of oscillator strength.

µ-Thin-layer chromatography coupled with laser ablation-inductively coupled plasma-mass spectrometry using tin(II)-imprinted polymer nanoparticles as a stationary phase for speciation of tin.

A unique and novel µ-thin-layer chromatography method based on Sn(II) ion-imprinted polymer (Sn-IIP) for speciation of tin ion species in water and plasma samples is introduced for the first time. For this purpose, N-allylthiourea (NATU) and ethylene glycol dimethacrylate (EGDMA) were copolymerized in the presence of Sn(II). The obtained polymer particles were identified using multiple techniques like BET, FT-IR, XRD, and FESEM. The effects of different variables such as pH of the solution, mobile phase composition, and IIP per CaSO4 mass ratio on the separation efficiency were also evaluated. After completion of the separation process on the plate, its surface was scanned by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Under the established optimal condition, the detection limit, relative standard deviation (RSD) of responses, and linear dynamic range (LDR) of the method were obtained as 0.3 µg L-1, 3.5%, and 0.8-900 µg L-1 for Sn(II) and 0.4 µg L-1, 4%, and 1-740 µg L-1 for Sn(IV) assay, respectively. The developed method was finally applied to the speciation of tin in various water and plasma samples. Graphical abstract Schematic representation of µ-thin-layer chromatography method based on tin(II) ion-imprinted polymer (Sn-IIP) for speciation of tin ion species in water and plasma samples and scanned separated casts by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS).

An enzyme-free sensing platform based on molecularly imprinted polymer/MWCNT composite for sub-micromolar-level determination of pyruvic acid as a cancer biomarker.

Pyruvic acid (PA) has been demonstrated to be an important cancer biomarker. Herein, carbon/carbon nanotube paste electrode was modified with the newly synthesized PA-imprinted polymer (MIP) and used as an enzyme-free sensor for PA assay. Methacrylic acid and ethylene glycol dimethacrylate were copolymerized in the presence of PA to prepare PA-IP. The MIP was characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. To analyze PA by the MIP/CNT-CP electrode, the electrode was incubated in the PA solution for a constant time and then, the anodic differential pulse voltammetry signal was recorded. Both extraction and electrochemical determination solutions were the same, making the procedure simple and fast. Presence of the CNT in the MIP electrode led to a great enhancement in the PA signal. The MIP material not only pre-concentrated PA at the electrode surface but also increased the electron-exchange rate. This was confirmed by electrochemical impedance spectroscopy. The effects of electrode composition, extraction condition, and voltammetry parameters on the sensing efficiency were optimized. Dynamic linear range, detection limit, and RSD of the sensor were estimated to be 0.1-200 µM, 0.048 µM (S/N), and 3.6% (n = 3), respectively. The utility of the method was confirmed by appropriate analysis results obtained for the determination of PA in the plasma and urine samples. Graphical Abstract.

A new bio-compatible Cd2+-selective nanostructured fluorescent imprinted polymer for cadmium ion sensing in aqueous media and its application in bio imaging in Vero cells.

Cadmium is a very toxic element found in various aqueous samples. The majority of the highly selective fluorescent ligands, designed for cadmium ion sensing, are hydrophobic compounds, thus making them inactive in aqueous media. Fluorescent imprinted polymers, synthesized by the proficient combination of hydrophilic functional monomers and hydrophobic ligands, may give a new and highly selective opportunity for utilizing most fluorescent ligands for toxic metal ion sensing in aqueous media. A novel fluorescent Cd2+-imprinted polymer was synthesized based on the co-polymerization of a mixture of acryl amide, vinyl benzene and ethylene glycol dimethacrylate in the presence of a 5-((3-hydroxynaphthalen-2-yl)methylene)pyrimidine-2,4,6(1,3,5)-trione (HMPT)-Cd2+ complex. The polymer was characterized by FT-IR spectroscopy, scanning electron microscopy and thermogravimetric analysis. Cadmium ion recognition by IIP created a new emission peak at about 502 nm based on the ICT mechanism, which was different from the emission peak of IIP in the absence of Cd2+ (440 nm). The non-imprinted polymer showed a fluorescence emission at about 500 nm, which was not affected by Cd2+, highlighting the recognition sites of IIP. The opto-sensor (IIP) exhibited a dynamic linear response range of 10-0.05 µM with the limit of detection (LOD) and quantification (LOQ) of 12.3 and 41 nM, respectively. Also, the relative standard deviation (RSD) of 3 separate determinations was 3.68%. Moreover, the developed chemosensor was highly selective for Cd2+ since the IIP fluorescence was not affected by the presence of other metal ions such as Zn2+, Cu+, Mn2+, Co2+, Ni2+, and Pb2+. The synthesized IIP can be used as a fluorescent probe for cadmium detection in live cells because of its minor cytotoxic effect on them.

A Nanostructured Microfluidic Artificial Olfaction for Organic Vapors Recognition.

Selective and sensitive detection of volatile organic compounds (VOCs) is of great importance in applications involving monitoring of hazardous chemicals or non-invasive diagnosis. Here, polymethyl methacrylate nanoparticles with acetone recognition sites are synthesized and integrated into a 3D-printed microfluidic platform to enhance the selectivity of the device. The proposed microfluidic-based olfaction system includes two parylene C-coated microchannels, with or without polymer nanoparticles. The two channels are exposed to 200, 400, 800, 2000, and 4000 ppm of VOCs (methanol, ethanol, acetone, acetonitrile, butanone, and toluene), and sensor responses are compared using a 2D feature extraction method. Compared to current microfluidic-based olfaction systems, responses observed between coated and uncoated channels showed an increased recognition capability among VOCs (especially with respect to acetone), indicating the potential of this approach to increase and fine-tune the selectivity of microfluidic gas sensors.

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.

Molecularly Imprinted Polymer Materials as Selective Recognition Sorbents for Explosives: A Review.

Explosives are of significant interest to homeland security departments and forensic investigations. Fast, sensitive and selective detection of these chemicals is of great concern for security purposes as well as for triage and decontamination in contaminated areas. To this end, selective sorbents with fast binding kinetics and high binding capacity, either in combination with a sensor transducer or a sampling/sample-preparation method, are required. Molecularly imprinted polymers (MIPs) show promise as cost-effective and rugged artificial selective sorbents, which have a wide variety of applications. This manuscript reviews the innovative strategies developed in 57 manuscripts (published from 2006 to 2019) to use MIP materials for explosives. To the best of our knowledge, there are currently no commercially available MIP-modified sensors or sample preparation methods for explosives in the market. We believe that this review provides information to give insight into the future prospects and potential commercialization of such materials. We warn the readers of the hazards of working with explosives.

Graphite/Ag/AgCl nanocomposite as a new and highly efficient electrocatalyst for selective electroxidation of oxalic acid and its assay in real samples.

Herein, graphite/Ag/AgCl nanocomposite is introduced as a new electrocatalyst material for the electrocatalytic oxidation of oxalic acid. Graphite/Ag/AgCl was synthesized by electroless deposition of nano-sized metallic silver and then silver chloride on graphite powder. The material obtained was characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and Energy-dispersive X-ray spectroscopy. The nanocomposite was mixed with n-eicosane as binder and used as carbon paste electrode for electrocatalytic oxidation of oxalic acid (OA). The graphite/Ag/AgCl nanocomposite electrode showed good catalytic activity for the electroxidation of oxalic acid in H3PO4 solution (0.05 mol L-1), leading to a distinct decrease in anodic overpotential (100 mV) and a substantial increase in anodic peak current (about 10 times), in comparison with the unmodified carbon paste electrode. Using the developed nanocomposite electrode and differential pulse voltammetry method, it became possible to determine oxalic acid in the concentration range of 0.01-0.75 mmol L-1 with detection limit of 3.7 × 10-6 mol L-1. The electrode showed very high sensitivity of 1341.3 µA mM-1 cm-2 which is remarkably better than the previously reported oxalic acid sensors. Thanks to high sensitivity and good selectivity of the electrode, the proposed method was successfully applied for the determination of OA in human urine and spinach samples. The satisfactory results obtained, confirmed the applicability of this sensor in the practical analysis.

A selective chemiresistive sensor for the cancer-related volatile organic compound hexanal by using molecularly imprinted polymers and multiwalled carbon nanotubes.

A chemiresistive sensor is described for the lung cancer biomarker hexanal. A composite consisting of molecularly imprinted polymer nanoparticles and multiwalled carbon nanotubes was used in the sensor that is typically operated at a voltage of 4 V and is capable of selectively sensing gaseous hexanal at room temperature. It works in the 10 to 200 ppm concentration range and has a 10 ppm detection limit (at S/N = 3). The sensor signal recovers to a value close to its starting value without the need for heating even after exposure to relatively high levels of hexanal. Graphical abstract Schematic presentation of a chemiresistive sensor for detection of hexanal, a cancer biomarker. The hexanal-imprinted polymeric nanoparticles were synthesized, mixed with multiwalled carbon nanotubes and coated on the surface of an interdigitated electrode to produce a nanocomposite chemiresistor gas sensor for hexanal.

Molecularly imprinted polymer nano-sphere/multi-walled carbon nanotube coated glassy carbon electrode as an ultra-sensitive voltammetric sensor for picomolar level determination of RDX.

An ultrasensitive and highly selective voltammetric sensor with ultra-trace level detection limit is introduced for RDX determination in water samples. The sensing platform is the nano-sized molecularly imprinted polymer (nano-MIP)/MWCNTs nanocomposite, casted on glassy carbon electrode (GCE). The MIP was synthesized by copolymerization of methacrylic acid and ethylene glycol dimethacrylate in the presence of RDX via precipitation polymerization. The MIP was characterized by scanning electron microscopy (SEM) and fast fourier transform infrared spectroscopy (FT-IR). It was demonstrated that the MIP, coated on the electrode, have the capability to adsorb RDX and increase its related voltammetric signal. This capability was remarkably lower, for the non-imprinted polymer (NIP)-based electrode. The MIP-based electrode signal to RDX is greatly enhanced in the presence of MWCNTs. The sensor showed excellent selectivity to RDX, compared to similar compounds of HMX and TNT. It exhibited two dynamic linear ranges including 0.1-10.0 nmol L-1 and 0.01-1.00 µmol L-1. The detection limit and relative standard deviation of the sensor were calculated to be 20 pmol L-1(3Sb/m, first curve) and 4.5% (10 nmol L-1, n = 5), respectively. The utility of the sensor was checked for RDX analysis in water samples which led to satisfactory results.