Ligand exchange based paraoxon imprınted QCM sensor

In the present work, a paraoxon imprinted QCM sensor has been developed for the determination of paraoxon based on the modification of paraoxon imprinted film onto a quartz crystal combining the advantages of high selectivity of the piezoelectric microgravimetry using MIP film technique and high sensitivity of QCM detection. The paraoxon selective memories have formed on QCM electrode surface by using a new metal–chelate interaction based on pre-organized monomer and the paraoxon recognition activity of these molecular memories was investigated. Molecular imprinted polymer (MIP) film for the detection of paraoxon was developed and the analytical performance of paraoxon imprinted sensor was studied. The molecular imprinted polymer were characterized by FTIR measurements. Paraoxon imprinted sensor was characterized with AFM and ellipsometer. The study also includes the measurement of binding interaction of paraoxon imprinted quartz crystal microbalance (QCM) sensor, selectivity experiments and analytical performance of QCM electrode. The detection limit and the affinity constant (K_affinity) were found to be 0.06 μM and 2.25 × 10⁴ M^? 1 for paraoxon [MAAP–Cu(II)–paraoxon] based thin film, respectively. Also, it has been observed that the selectivity of the prepared paraoxon imprinted sensor is high compared to a similar chemical structure which is parathion.     

Molecular-imprinted, polymer-coated quartz crystal microbalances for the detection of terpenes

A piezoelectric sensor coated with an artificial biomimetic recognition element has been developed for the determination of L-menthol in the liquid phase. A highly specific noncovalently imprinted polymer (MIP) was cast in situ on to the surface of a gold-coated quartz crystal microbalance (QCM) electrode as a thin permeable film. Selective rebinding of the target analyte was observed as a frequency shift quantified by piezoelectric microgravimetry with the QCM. The detectability of L-menthol was 200 ppb with a response range of 0-1.0 ppm. The response of the MIP-QCM to a range of monoterpenes was investigated with the sensor binding menthol in favor of analogous compounds. The sensor was able to distinguish between the D- and L-enantiomers of menthol owing to the enantioselectivity of the imprinted sites. To our knowledge, this is the first report describing enantiomeric resolution within an MIP utilizing a single monomer-functional moiety interaction. It is envisaged that this technique could be employed to determine the concentration of terpenes in the atmosphere.     

Comparison of different methodologies for integration of molecularly imprinted polymer and electrochemical transducer in order to develop a paraoxon voltammetric sensor

In this work a paraoxon voltammetric sensor was introduced. Different methods for integration of molecularly imprinted polymer (MIP) and electrochemical transducer were investigated. Three techniques including MIP particles embedding in the carbon paste (CP) (MIP-CP), coupling of MIP with the glassy carbon electrode (GC) surface by using poly epychloro hydrine (PECH) (MIP/PECH-GC) and MIP/graphite mixture thin layer attachment onto the glassy carbon electrode (MIP/Graphite-PECH-GC) were tested. The prepared electrodes were applied for paraoxon measurement by using a three-step procedure including analyte extraction in the electrode, electrode washing and electrochemical measurement of paraoxon. The washing of electrodes, after paraoxon extraction, led to high selectivity of electrode for paraoxon. It was found that MIP-CP electrode had higher response to paraoxon in comparison to other tested electrodes. Besides, the washing process decreased response magnitude of MIP/PECH-GC and MIP/Graphite-PECH-GC but, the response of MIP-CP was not affected considerably by the washing. Parathion was chosen to evaluate the selectivity of MIP based sensors. It was proved that the MIP-CP had better selectivity, wider linear range and lower detection limit in comparison to other tested electrodes. The developed MIP-CP electrode was used as a high selective sensor for paraoxon determination in water and vegetable samples.     

Quartz crystal microbalance sensor for organic vapor detection based on molecularly imprinted polymers

Molecularly imprinted polymers on quartz crystal microbalances (QCM) are examined for their ability to detect vapors of small organic molecules with greater sensitivity and selectivity than the traditional amorphous polymer coatings. Hydroquinone and phenol serve as noncovalently bound templates that generate shape-selective cavities in a poly(acrylic) or poly(methacrylic) polymer matrix. The imprinted polymers are immobilized on the piezoelectric crystal surface via a precoated poly(isobutylene) layer. The behavior of the imprinted polymer films is characterized by the dynamic and steady-state response of the QCM frequency to pulses of organic vapors in dry air. The apparent partition coefficients are determined for imprinted and nonimprinted polymers prepared by two synthetic methods and for varying mole ratios of template to monomer. The hydroquinone-imprinted polymers and, to a lesser extent, the phenol-imprinted polymers exhibit greater sensitivity and higher selectivity than the nonimprinted polymers toward organic vapors that are structurally related to the templates. These results indicate that molecularly imprinted polymers are promising for the development of selective piezoelectric sensors for organic vapor detection.     

Electropolymerized molecularly imprinted polymer films of a bis-terthiophene dendron: folic acid quartz crystal microbalance sensing

A folic acid sensor was prepared via an electropolymerized molecularly imprinted polymer (E-MIP) film of a bis-terthiophene dendron on a quartz crystal microbalance (QCM). The cyclic voltammetry (CV) electrodeposition of the imprinted polymer film was monitored by electrochemical QCM or E-QCM, enabling in situ monitoring and characterization of E-MIP film formation and the viscoelastic behavior of the film. A key component of the E-MIP process is the use of a bifunctional monomer design to precomplex with the template and function as a cross-linker. The complex was electropolymerized and cross-linked by CV to form a polythiophene matrix. Stable cavities were formed that specifically fit the size and shape of the folic acid template. The same substrate surface was used for folic acid sensing. The predicted geometry of the 1:2 folic acid/terthiophene complex was obtained through semiempirical AM1 quantum calculations. The analytical performance, expressed through the figures of merit, of the sensor in aqueous solutions of the analyte was investigated. A relatively good linearity, R(2) = 0.985, was obtained within the concentration range 0-100 μM folic acid. The detection limit was found to be equal to 15.4 μM (6.8 μg). The relative cross selectivity of the folic acid imprinted polymer against the three molecules follows this trend: pteroic acid (= 50%) > caffeine (= 41%) > theophylline (= 6%). The potential and limitations of the E-MIP method were also discussed.     

Fabrication,characterization and sensing properties of Cu(II) ion imprinted sol–gel thin film on QCM

Cu(II)-molecularly imprinted sol–gel films (Cu(II)-MISGF), coated on a quartz crystal microbalance (QCM) chip, were fabricated using a sol–gel procedure. Co-hydrolysis and co-condensation of Cu(II) (templates), 3-aminopropyltrimethoxysilane (APTS, functional monomer) and tetraethoxysilane (TEOS, cross-linking agent) were performed with acid and base catalysis. The properties of the Cu(II)-MISGF were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and the electrochemical methods of cyclic voltammetry (CV). Microstructural observations revealed that the acid-catalyzed system yielded more mechanically stable thin films. A combined Cu(II)-MISGF-QCM with flow injection analysis (FIA) method was utilized to investigate the sensing performance of the Cu(II)-MISGF, with special emphasis on the most important properties of sensitivity, selectivity and response time. The Cu(II)-MISGF-QCM sensor, at a TEOS/APTS molar ratio of 10, exhibited excellent selectivity and rapidly responded to Cu(II) ions.     

Imprinting of nucleotide and monosaccharide recognition sites in acrylamidephenylboronic acid-acrylamide copolymer membranes associated with electronic transducers

Molecular recognition sites for the nucleotides adenosine 5'-monophosphate (1), guanosine 5'-monophosphate (2), cytosine 5'-monophosphate (3), and uridine 5'-monophosphate (4) are imprinted in an acrylamide-acrylamidephenylboronic acid copolymer (5) membrane. The imprinted membranes are assembled on piezoelectric Au quartz crystals or Au electrodes via electropolymerization or on the gate surface of an ISFET device by radical polymerization. The imprinted membranes reveal selectivity toward the imprinted nucleotide, and the association of the respective nucleotides with the recognition sites is transduced by the following: (i) microgravimetric, quartz crystal microbalance (QCM) measurements; (ii) Faradaic impedance analyses, and (iii) potentiometric responses of the ISFET devices. While the microgravimetric QCM measurements reflect the swelling of the polymers upon the association of the nucleotides with the recognition sites, the ISFET response is due to the charging of the polymer membrane as a result of the formation of the nucleotide-boronate complex. The selective detection of the nucleotides may lead to new DNA/RNA sequencing methods. Also, specific recognition sites for beta-D(+)-glucose (6), D(+)-galactose (7), and beta-D(-)-fructose (8) were imprinted in an acrylamide-acrylamidephenylboronic acid copolymer (5) membrane associated with an ISFET device. Selective sensing of the respective monosaccharides is accomplished in the presence of the imprinted membrane-functionalized ISFET devices.     

A real time detection of the ovarian tumor associated antigen 1 (OVTA 1) in human serum by quartz crystal microbalance immobilized with anti-OVTA 1 polyclonal chicken IgY antibodies

In this study, we developed a sensitive quartz crystal microbalance (QCM) sensor which employs the anti-ovarian tumor associated antigen 1 (OVTA 1) IgY polyclonal chicken antibodies on the crystal surface for the detection of OVTA 1 in human serum. The anti-OVTA 1 IgY antibodies were anchored on the thiol-activated sensor surface using 1-ethyl-3[3-dimethylaminopropyl] carbodiimide hydrochloride/N-hydroxysuccinimide (EDC–NHS) coupling. The responses for different concentrations of anti-OVTA 1 antibody were also studied and 40 μg/mL was favorable for homogenous antibody coverage. The QCM sensor was used to monitor both immobilization and the target binding affinity. The anti-OVTA 1 antibody based QCM has allowed the competent detection of OVTA 1 in a high linear range of 0.5–10 μg/mL. The total time needed to complete the detection was as short as 5–6 h. The regeneration studies demonstrated that the proposed sensor was reusable up to 9 cycles with a slight loss in binding affinity. The detection of OVTA 1 in human serum allows a potential exploitation of the anti-OVTA 1 polyclonal antibody based QCM immunoassay for the screening of OVTA 1 antigen.     

Photoderivatized polymer thin films at quartz crystal microbalance surfaces: sensors for carbohydrate-protein interactions

Photoderivatized polymer-coated gold surfaces have been developed following a perfluorophenylazide-based double ligation strategy. Gold-plated quartz crystal microbalance (QCM) crystals were initially covalently functionalized with a monolayer of poly(ethylene glycol) (PEG), using photo- or thermolytic nitrene formation and insertion. The polymer surfaces were subsequently used as substrates for photoinsertion of carbohydrate-derivatized photoprobes, yielding different recognition motifs for selective protein binding. The resulting robust and biocompatible sensor surfaces were applied to a flow-through QCM instrument for monitoring lectin-carbohydrate interactions in real time. The results clearly show the predicted lectin selectivity, demonstrating the applicability of the approach.     

A quartz crystal microbalance-based sensor system coated with functional polymers for SO2 and NO2 detection

In this work, a quartz crystal microbalance (QCM)-based adsorption sensor system with high sensitivity, selectivity, and reproducibility is designed and fabricated. The functional polymers such as polypyrrole, poly(3,4-ethylenedioxythiophene) (PEDOT), and polystyrene are coated on 8 MHz AT-cut quartz crystal surfaces as sensing materials for SO2 and NO2. All sensing materials on the QCM surface are characterized experimentally by SEM and AFM. The frequency shifts of the QCM by adsorption and desorption of gases are measured and analyzed to assess the practical applicability of the sensor system. The overall results show that the QCM coated with polypyrrole is highly selective for SO2 gas and that coated with PEDOT is for NO2. It is proven that the QCM-based adsorption sensor system is possible for monitoring SO2 and NO2 gases in the mixture of ppm level.     

Measurement of polystyrene photodegradation rate using a quartz crystal microbalance

Polystyrene is a very popular polymer utilised in the manufacture of various consumer products. This polymer is very cheap; however, after its usage, the slowness of its photodegradation leads to environmental pollution. In this report, the author presents a technique to systematically measure the rate of photodegradation of a thin polystyrene film. The said film was made to coat a quartz crystal microbalance (QCM) sensor. In order to detect polymer degradation and the reduction in the molecular weight, the resonance frequency of the sensor was monitored for 24 h. Results revealed that QCM sensor irradiation with ultraviolet light with a wavelength of 365 nm and optical power of 1.5 mW caused a quite significant change in the polymer structure.     

A new polysiloxane coating on QCM sensor for DMMP vapor detection

A new material-poly{methyl [3-(2-hydroxyl, 4,6-bistrifluoromethyl)phenyl]propylsiloxane} (PMTFMPS), which was sensitive to toxic organophosphate vapor, was synthesized via O-alkylation, claisen rearrange reaction and hydrosilylation reaction. The polymer was coated on quartz crystal microbalance (QCM) to investigate its gas sensitive properties to nerve agents’ simulant dimethyl methylphosphonate (DMMP) vapor, as well as other interfering vapors. It was found that QCM sensor responded linearly to DMMP vapor with a slope of 27 Hz/ppm in the 10–50 ppm range. The material was much more sensitive to DMMP than to other interfering vapors, thus high selectivity to DMMP was demonstrated. The influence of humidity on the sensor response was also examined. The results showed that the frequency shifts were about 60% when tested in 77% RH wet air than in dry N₂. When compared with our previously studied unfluorinated phenol-modified siloxane PMPS, PMTFMPS exhibited sensitivity enhancement of 2.3 times and an increased resistance to humidity variations.     

Recognition of dengue virus protein using epitope-mediated molecularly imprinted film

Molecularly imprinted film was fabricated in the presence of a pentadecapeptide onto a quartz crystal microbalance (QCM) chip. This 15-mer peptide has been known as the linear epitope of the dengue virus NS1 protein. Imprinting resulted in an increased polymer affinity toward the corresponding templates but also to the virus protein. Direct detection of the dengue virus protein was achieved quantitatively. The QCM chip response to the NS1 protein was obtained using epitope-mediated imprinting demonstrating a comparable frequency shift in chips immobilized with monoclonal antibodies. The binding effect was further enhanced and confirmed using a monoclonal antibody to form a sandwich with the MIP-NS1 protein complex on the chip. No pretreatment was required.     

A novel technique to immobilize DNA on surface of a quartz crystal microbalance by plasma treatment and graft polymerization

A quartz crystal microbalance (QCM) is well known to provide mass-sensitive devices in nanogram levels, because of the resonance frequency changes upon the adsorption on the electrode. It offers the possibility of monitoring hybridization in real time and with high selectivity. In this study, a biosensor system was developed for the detection of Vibrio parahaemolyticus via its oligonucleotide probe immobilized on the gold electrodes' surface of QCM. However, because the surface of QCM was an inorganic substance, it was difficult to immobilize the oligonucleotide probe. In this study, the plasma surface modification of QCM through deposition of hexamethyldisilazane (HMDSZ) films as an interlayer was investigated. The interlayer provided good adhesion to the substrate and had a uniform structure. The result indicates that plasma deposition was a useful technique to immobilize the oligonucleotide probe on the gold electrodes' surface via glutaraldehyde (GA) coupling. To improve immobilization, post treatments by surface grafting of acrylamide (AAm) and polyethyleneimine (PEI) treatment onto the electrodes were also performed. The result demonstrates that the shift of resonance frequency of QCM was improved via subsequent graft polymerization of AAm and PEI treatment onto the electrodes. The QCM sensor after plasma deposition and surface modification could provide detection sensitivity up to 86 ng/ml and kept at 88% detecting sensitivity after 19 days of storage at 0 °C. After washing with 0.1 M NaOH solution and 7 times of repeated use in detecting, the regeneration rate of QCM could be up to 60%.     

Directly fast detection of digoxin in the serum sample by the synthetic receptor sensor

A novel biosensor (the synthetic receptor sensor) employing the molecular imprinted technology for the digoxin analysis is investigated. The molecularly imprinted polymer (MIP) modified electrode can specifically bind to the analyte in the sample without sample pretreatment. The digoxin analyzed by the MIP sensor was carried out in 1 mM K₃Fe(CN)₆ solution with the cyclic voltammetry. In the system, the K₃Fe(CN)₆³⁻/Fe₂(CN)₆⁴⁻ redox couple was taking place. When the solution contains the digoxin, the MIP on the electrode will bind the digoxin. Further the redox system is interrupted and the peak current is decreased according to the digoxin concentration increasing. Digoxin is a glycosylated steroid-like drug. It is important for the heart disease treatment. However, since the digoxin toxic level is low, the drug remains in the blood sample must be monitored frequently. The device possesses many advantages, such as high specific recognition properties, good chemical and mechanical stability, simplicity and low cost of preparation, sensitive and label free determination. The reproducibility is good (CV < 5). The linear relationship between the digoxin concentration and the current is 1.28–128 nM, and a detection limit of 1.28 nM is achieved. The detection time is less than 5 min.     

Atrazine sensor based on molecularly imprinted polymer-modified gold electrode

Molecularly imprinted polymers (MIP) have been elucidated to work as artificial receptors. In our present study, a MIP was applied as a molecular recognition element to a chemical sensor. We have constructed an atrazine sensor based on a MIP layer selective for atrazine and its electrochemical reduction on gold electrode. The atrazine sensor was fabricated by directly polymerizing the atrazine-imprinted polymer composed from methacrylic acid and ethylene glycol dimethacrylate onto the surface of a gold electrode. By introducing LiCl into the MIP, atrazine was reduced below -800 mV vs Ag/AgCl reference electrode, at pH 3. The cathodic current of atrazine depended on the concentration of atrazine at the range of 1-10 microM. The sensor exhibited a selective response to atrazine. A nonimprinted polymer-modified electrode did not show selective response to atrazine, thus implying that the imprinted polymer acts as recognition element of atrazine sensor.     

Molecularly imprinted polymer for the recognition of biological warfare agent staphylococcal enterotoxin B based on Surface Plasmon Resonance

Molecularly imprinted polymers (MIPs) embody a new class of materials possessing high selectivity and affinity for the target molecules. The aim of the present work is to explore the feasibility of employing the MIP as sensing material for the detection of Staphylococcal enterotoxin B (SEB) by Surface Plasmon Resonance (SPR). In this context, the MIP film was prepared by in-situ electropolymerization of 3-aminophenylboronicacid (3-APBA) on the bare gold chip in the presence of SEB molecule. The MIP of SEB exhibited a linear response from 3.2 fM to 25.6 fM (r² = 0.99) with a detection limit of 0.05 fM. K_D (equilibrium constant) and Bmax (maximum binding capacity of analyte) were calculated by using kinetic evaluation software and found to be 24 fM and 71, respectively and change in Gibb's free energy (?G) value calculated using Vant's Hoff equation was found to be −77.54 kJ/mol. Interference study was performed with the homologs of SEB such as SEA and SEC in order to know the selectivity efficiency of SEB MIP and were found to be 23.57% and 23.43%, respectively.     

Kinetics of photocatalytic reduction of Pb(II) on nanocrystalline TiO2 coatings: A quartz crystal microbalance study

Pb(II) is a highly toxic substance, exposure to which can cause various diseases. To better understand the application of TiO₂ as a photocatalyst for removing Pb(II) from wastewater, quartz crystal microbalance (QCM) technique was employed to in situ investigate the reduction behavior of Pb(II) on nanocrystalline TiO₂ coatings under N₂. The processes of Pb(II) reduction at various concentrations of HCOOH and in the presence of different organic additives were monitored, and the corresponding kinetics was proposed. The obtained results showed that the kinetics of Pb(II) reduction on TiO₂ coatings was closely related to the organic additives. The HCOOH showed a higher efficiency for Pb(II) reduction in comparison with other organic additives, and the reduction-rate constant reached 0.54 × 10⁻³ s⁻¹ which was two times higher than that exhibited in the presence of C₂H₅OH. QCM measurement provides an useful method for monitoring the reduction process of Pb(II) on TiO₂ coatings.     

Synthesis and evaluation of a molecularly imprinted polymer for selective on-line solid-phase extraction of 4-nitrophenol from environmental water

A molecularly imprinted polymer (MIP) able to bind 4-nitrophenol (4-NP) was prepared using noncovalent molecular imprinting methods and evaluated as a selective sorbent in molecularly imprinted solid-phase extraction (MISPE) on-line coupled to a reversed-phase HPLC. It has been shown that the conditions chosen for washing the MIP and for eluting the analyte in the MISPE process are extremely important for ensuring good selectivity and recovery. River water samples, spiked with the 11 Environmental Protection Agency phenolic compounds at microgram per liter levels, were preconcentrated on-line using this MIP, and 4-NP was selectively extracted. The humic acid interference was simultaneously reduced considerably. The MIP was also compared with a commercially available highly cross-linked polymer (LiChrolut EN) and the former yielded cleaner extracts.     

Development of piroxicam sensor based on molecular imprinted polymer-modified carbon paste electrode

A new voltammetric sensor for piroxicam measurement is introduced. A piroxicam-selective molecularly imprinted polymer (MIP) and a non-imprinted polymer (NIP) were synthesized in a non-covalent approach using methacrylic acid (MAA) as functional monomer and ethylene glycol dimethacrylate (EGDMA) as cross-linking monomer via a free radical polymerization and then was used for carbon paste (CP) electrode preparation. The MIP, embedded in the carbon paste electrode, functioned as a selective recognition element and pre-concentrator agent for piroxicam determination. The prepared electrode was used for piroxicam measurement via a three-step procedure including analyte extraction in the electrode, electrode washing and electrochemical measurement of piroxicam. The MIP–CP electrode showed good recognition ability in comparison to NIP–CP. Some parameters affecting sensor response were optimized. Under optimum conditions the oxidation peak current was proportional to piroxicam concentration over the range 2–190 and 190–2500 nM. The detection limit was found to be 0.5 nM. This sensor has been successfully applied for the determination of piroxicam in pharmaceutical formulations and serum samples.