Krzysztof Noworyta

Imprinted polymer-based enantioselective acoustic sensor using a quartz crystal microbalance

An enantioselective chemical sensor has been designed and fabricated. The sensor is based on a molecularly imprinted polymer, serving as the recognition element, and a quartz crystal microbalance (QCM), used as the transducer. The polymer, imprinted with the chiral β-blocking drug S-propranolol, was cast as a thin permeable film onto a gold electrode deposited on the quartz crystal vibrator. The mass increase of the polymer due to analyte binding was quantified by piezoelectric microgravimetry with the QCM. The sensor was able to discriminate between the R- and S-propranolol enantiomers in acidified acetonitrile solutions owing to the enantioselectivity of the imprinted sites. Detectability of S-propranolol was 50 µmol dm–3. The general procedure developed here for preparation of the sensor can be adapted for fabrication of a range of different stable analytical sensing devices for numerous analytes by using conventional molecular imprinting protocols.

Study of Redox Active C 60 / Pd Films by Simultaneous Cyclic Voltammetry and Piezoelectric Microgravimetry at an Electrochemical Quartz Crystal Microbalance

The formation and properties of redox active C 60 /Pd films on gold electrodes of quartz oscillators were investigated by simultaneous cyclic voltammetry and piezoelectric microgravimetry at a quartz crystal microbalance. The films were prepared by electroreduction of solutions of C 60 and [Pd II (CH 3 COO) 2 ] 3 in 0.1 mol dm -3 tetra(n-butyl)ammonium perchlorate in acetonitrile-toluene (1:4, v:v). The composition of the solution from which the films were prepared significantly influenced the pattern of the film growth. The present results confirm that palladium clusters are codeposited with the C 60 /Pd film if the palladium complex to C 60 ratio was high. The reduced polymer film becomes partially electrochemically inactive at a sufficiently negative potential range. However, this electrically inactive film can be oxidized at very positive potentials. For charge compensation, the tetra(n-butyl)ammonium countercations enter the film during its electroreduction and are expelled from the film during electro-oxidation. At relatively high potential scan rates, only the outermost layers of the film that are in direct contact with the bathing solution are electrochemically active. At low scan rates, however, the bulk film material is also active. At very negative potentials, the film is removed from the electrode. The size of the tetra(n-alkyl)ammonium countercation is a major factor that determines both the electrochemical properties of the C 60 /Pd films and their stability with respect to dissolution.

Molecular recognition of adenine, adenosine and ATP at the air–water interface by a uracil appended fullerene

A new C60-uracil adduct capable of hydrogen bonding, via complimentary base pairing, of adenine, adenosine, and adenosine 5′-triphosphate (ATP) was synthesized and characterized by UV-visible and 1H NMR spectroscopy, cyclic voltammetry and differential pulse voltammetry, as well as ESI-mass spectrometry. Molecular modeling by ab initio B3LYP/3–21G(*) calculations revealed the Watson–Crick type base pairing. Stable “expanded liquid” Langmuir films of the C60-uracil–adenine, C60-uracil–adenosine and C60-uracil–ATP complexes were prepared and characterized by isotherms of surface pressure versus area per molecule as well as the Brewster angle microscopy imaging. The area per molecule at infinite adduct dilution in the film was dependent on composition of the subphase solution and increased in the order: water < adenine < adenosine < ATP solution. Comparison of experimental and calculated areas per molecule and dipole moment components normal to the subphase–air interface indicated prevailing horizontal orientation of the complexes in the films. The Langmuir films were transferred, by using the Langmuir–Blodgett technique, onto quartz slides and characterized by the UV-visible spectroscopy.

Molecularly imprinted polymers for separating and sensing of macromolecular compounds and microorganisms.

The present review article focuses on gathering, summarizing, and critically evaluating the results of the last decade on separating and sensing macromolecular compounds and microorganisms with the use of molecularly imprinted polymer (MIP) synthetic receptors. Macromolecules play an important role in biology and are termed that way to contrast them from micromolecules. The former are large and complex molecules with relatively high molecular weights. The article mainly considers chemical sensing of deoxyribonucleic acids (DNAs), proteins and protein fragments as well as sugars and oligosaccharides. Moreover, it briefly discusses fabrication of chemosensors for determination of bacteria and viruses that can ultimately be considered as extremely large macromolecules.

Structure and properties of C60–Pd films formed by electroreduction of C60 and palladium(II) acetate trimer: evidence for the presence of palladium nanoparticles

The composition, surface morphology, structure, and electrochemical properties of thin solid films of the polymer, C60–Pd, were studied by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), and energy dispersive X-ray fluorescence (EDXRF) as well as being examined by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) with selective area diffraction (SAD) and by cyclic voltammetry (CV), respectively. The C60–Pd films were deposited onto Au or Pt electrodes by electroreductive co-polymerization of C60 and the palladium(II) acetate trimer, [Pd(ac)2]3, in a mixed acetonitrile–toluene (4∶1, v/v) solution of 0.1 M tetra(n-butyl)ammonium perchlorate under multicyclic voltammetry or potentiostatic conditions. The structure and composition of the C60–Pd films were dependent on the relative concentration of the polymer precursors, i.e., C60 and [Pd(ac)2]3, in the solution for electropolymerization. That is, in films grown in solutions with a high [Pd(ac)2]3∶C60 ratio, (–C60–Pd–)n polymeric chains were separated by the Pd nanoclusters. These films were relatively smooth and uniform. In contrast, films electropolymerized in solutions with a low [Pd(ac)2]3∶C60 ratio were rough, porous and much less uniform. The presence of the Pd nanoclusters in the C60–Pd film influenced the electrode processes of probing redox species dissolved in solution. That is, electro-oxidation of an N,N,N′,N′-tetramethyl-1,4-phenylenediamine (TMPDA) electrochemical redox probe was partially inhibited at the electrode coated by the C60–Pd film with a relatively low Pd nanocluster content. In contrast, electro-oxidation of TMPDA was effectively mediated by the C60–Pd film containing appreciable amounts of dispersed Pd nanoclusters.

Extended-gate field-effect transistor (EG-FET) with molecularly imprinted polymer (MIP) film for selective inosine determination.

A novel recognition unit of chemical sensor for selective determination of the inosine, renal disfunction biomarker, was devised and prepared. For that purpose, inosine-templated molecularly imprinted polymer (MIP) film was deposited on an extended-gate field-effect transistor (EG-FET) signal transducing unit. The MIP film was prepared by electrochemical polymerization of bis(bithiophene) derivatives bearing cytosine and boronic acid substituents, in the presence of the inosine template and a thiophene cross-linker. After MIP film deposition, the template was removed, and was confirmed by UV-visible spectroscopy. Subsequently, the film composition was characterized by spectroscopic techniques, and its morphology and thickness were determined by AFM. The finally MIP film-coated extended-gate field-effect transistor (EG-FET) was used for signal transduction. This combination is not widely studied in the literature, despite the fact that it allows for facile integration of electrodeposited MIP film with FET transducer. The linear dynamic concentration range of the chemosensor was 0.5-50 μM with inosine detectability of 0.62 μM. The obtained detectability compares well to the levels of the inosine in body fluids which are in the range 0-2.9 µM for patients with diagnosed diabetic nephropathy, gout or hyperuricemia, and can reach 25 µM in certain cases. The imprinting factor for inosine, determined from piezomicrogravimetric experiments with use of the MIP film-coated quartz crystal resonator, was found to be 5.5. Higher selectivity for inosine with respect to common interferents was also achieved with the present molecularly engineered sensing element. The obtained analytical parameters of the devised chemosensor allow for its use for practical sample measurements.

Early diagnosis of fungal infections using piezomicrogravimetric and electric chemosensors based on polymers molecularly imprinted with d-arabitol

An elevated concentration of d-arabitol in urine, especially compared to that of l-arabitol or creatinine, is indicative of a fungal infection. For that purpose, we devised, fabricated, and tested chemical sensors determining d-arabitol. These chemosensors comprised the quartz crystal resonator (QCR) or extended-gate field-effect transistor (EG-FET) transducers integrated with molecularly imprinted polymer (MIP) film recognition units. To this end, we successfully applied a covalent approach to molecular imprinting, which involved formation of weak reversible covalent bonds between vicinal hydroxyl groups of arabitol and boronic acid substituents of the bithiophene functional monomer used. The MIP films were synthesized and simultaneously deposited on gold electrodes of quartz crystal resonators (Au-QCRs) or Au-glass slides by oxidative potentiodynamic electropolymerization. With the QCR and EG-FET chemosensors, the d-arabitol concentration was determined under flow-injection analysis and stagnant-solution binding conditions, respectively. Selectivity with respect to common interferences, and l-arabitol in particular, of the devised chemosensors was superior. Limits of detection and linear dynamic concentration ranges of the QCR and EG-FET chemosensors were 0.15 mM and 0.15 to 1.25 mM as well as 0.12 mM and 0.12 to 1.00 mM, respectively, being lower than the d-arabitol concentrations in urine of patients with invasive candidiasis (>220 μM). Therefore, the devised chemosensors are suitable for early diagnosis of fungal infections caused by Candida sp. yeasts.

Electrochemistry of Solutions as well as Simultaneous Cyclic Voltammetry and Piezoelectric Microgravimetry of Conducting Films of 2‐(n‐Alkyl)fulleropyrrolidines

Effects of alkyl chain length and protonation of the pyrrolidine nitrogen on the electrochemical behavior of 2-(n-alkyl)fulleropyrrolidines, C 60 pyr-C m (m = 4, 6, 8, 10, and 12), in solutions as well as in thin solid films are reported. Formal redox potentials of the first and second one-electron reversible electroreductions of C 60 pyr-C m in 0.1 mol dm -3 tetra(n-butyl)ammonium hexafluorophosphate in benzonitrile are shifted negatively by ca. 130 mV and that of the third electroreduction by ca. 240 mV with respect to the potentials of the corresponding C 60 redox couples. Protonation of the pyrrolidine nitrogen results in a positive shift of the formal redox potential of C 60 pyr-C m in solution by ca. 90 mV, indicating more pronounced electron deficiency of the C 60 cage. Simultaneous cyclic voltammetry and piezoelectric microgravimetry of the drop-coated thin solid films of C 60 pyr-C m in acetonitrile solutions reveals that the film solubility is larger the longer the alkyl chain and the more reduced the C 60 cage. Also, film stability with respect to dissolution is strongly dependent on the nature of the cation of the supporting electrolyte and acidity of solution. That is, the adduct films are more stable in the TBA + than Li + solutions, similar to that of pristine C 60 films. Moreover, electroreduction of the adduct films in acidified Li + solutions results in electrochemically inactive films.

Molecularly Imprinted Polymer (MIP) Film with Improved Surface Area Developed by Using Metal–Organic Framework (MOF) for Sensitive Lipocalin (NGAL) Determination

Electropolymerizable functional and cross-linking monomers were used to prepare conducting molecularly imprinted polymer film with improved surface area with the help of a sacrificial metal-organic framework (MOF). Subsequent dissolution of the MOF layer resulted in a surface developed MIP film. This surface enlargement increased the analyte accessibility to imprinted molecular cavities. Application of the porous MIP film as a recognition unit of an extended-gate field effect transistor (EG-FET) chemosensor effectively enhanced analytical current signals of determination of recombinant human neutrophil gelatinase-associated lipocalin (NGAL).

Potentiometric chemosensor for neopterin, a cancer biomarker, using an electrochemically synthesized molecularly imprinted polymer as the recognition unit.

With an established procedure of molecular imprinting, a synthetic polymer receptor for the neopterin cancer biomarker was devised and used as a recognition unit of a potentiometric chemosensor. For that, bis-bithiophene derivatized with cytosine and bithiophene derivatized with boronic acid were used as functional monomers. The open-circuit potential (OCP) based transduction under flow-injection analysis conditions (FIA) determined neopterin in the concentration range of 0.15-2.5mM with the 22 µM limit of detection (LOD) and 7.01(±0.15) mVmM(-1) sensitivity indicating its potential suitability in clinical analysis applications. The molecularly imprinted polymer (MIP) film showed an appreciable apparent imprinting factor of ~6. The chemosensor successfully discriminated the interferences including the 6-biopterin and pterin structural analogs of neopterin as well as glucose and creatinine. Moreover, it determined neopterin in synthetic serum samples.