Piezomicrogravimetric and impedimetric oligonucleotide biosensors using conducting polymers of biotinylated bis(2,2'-bithien-5-yl)methane as recognition units.

A new conducting polymer of biotinylated bis(2,2'-bithien-5-yl)methane was prepared and applied as the recognition unit of two different biosensors for selective oligonucleotide determination using either electrochemical impedance spectroscopy (EIS) or piezoelectric microgravimetry (PM) for label-free analytical signal transduction. For preparation of this unit, first, a biotinylated bis(2,2'-bithien-5-yl)methane functional monomer was designed and synthesized. Then, this monomer was potentiodynamically polymerized to form films on the surface of a glassy carbon electrode (GCE) and a Au electrode of a quartz crystal resonator (QCR) for the EIS and PM transduction, respectively. On top of these films, neutravidin was irreversibly immobilized by complexing the biotin moieties of the polymer. Finally, recognizing biotinylated oligonucleotide was attached by complexing the surface-immobilized neutravidin. This layer-by-layer assembling of the poly(thiophene-biotin)-neutravidin-(biotin-oligonucleotide) recognition film served to determine the target oligonucleotide via complementary nucleobase pairing. Under optimized determination conditions, the target oligonucleotide limit of detection (LOD) was 0.5 pM and 50 nM for the EIS and PM transduction, respectively. The sensor response to the target oligonucleotide was linear with respect to logarithm of the target oligonucleotide concentration in a wide range of 0.5 pM to 30 µM and with respect to its concentration in the range of 50 to 600 nM for the EIS and PM transduction, respectively. The biosensors were appreciably selective with respect to the nucleobase mismatched oligonucleotides.

Electrochemical sensor for selective tyramine determination, amplified by a molecularly imprinted polymer film.

A molecularly imprinted polymer (MIP) film based electrochemical sensor for selective determination of tyramine was devised, fabricated, and tested. Tyramine is generated in smoked and fermented food products. Therefore, it may serve as a marker of the rottenness of these products. Importantly, intake of large amounts of tyramine by patients treated with monoamine oxidase (MAO) inhibitors may lead to a "cheese effect", namely, a dangerous hypertensive crisis. The limit of detection at S/N = 3 of the chemosensor, in both differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) determinations, with the use of the Fe(CN)64-/Fe(CN)63- redox probe, was 159 and 168 µM tyramine, respectively. The linear dynamic concentration range was 290 µM to 2.64 mM tyramine. The chemosensor was highly selective with respect to the glucose, urea, and creatinine interferences. Its DPV determined apparent imprinting factor was 5.6. Moreover, the mechanism of the "gate effect" in the operation of the polymer film-coated electrodes was unraveled.

Direct determination of small RNAs using a biotinylated polythiophene impedimetric genosensor.

Herein, direct determination of small RNAs is described using a functional-polymer modified genosensor. The analytical strategy adopted involves deposition by electropolymerization of biotinylated polythiophene films on the surface of miniaturized, disposable, gold screen-printed electrodes, followed by the layer-by-layer deposition of streptavidin, and then biotynilated capture probes. A small RNA (miR-221) target was determined via the impedimetric measurement of the hybridization event in a label-free and PCR-free approach. Under optimized conditions, the limit of detection (LOD) was 0.7 pM miR-221 (15% RSD). The genosensor was applied for determination of miR-221 in total RNA extracted from human lung and breast cancer cell lines, discriminating between the cancer-positive and -negative cells, without any amplification step, in less than 2h.

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.

Nicotine molecularly imprinted polymer: synergy of coordination and hydrogen bonding.

Two new bis(2,2'-bithienyl)methane derivatives, one with the zinc phthalocyanine substituent (ZnPc-S16) and the other with the 2-hydroxyethyl substituent (EtOH-S4), were synthesized to serve as functional monomers for biomimetic recognition of nicotine (Nic) by molecular imprinting. Formation of a pre-polymerization complex of the Nic template with ZnPc-S16 and EtOH-S4 was confirmed by both the high negative Gibbs free energy gain, ΔG = -115.95 kJ/mol, calculated using the density functional theory at the B3LYP/3-21G* level, and the high stability constant, Ks = 4.67 × 10(5) M(-1), determined by UV-vis titration in chloroform. A solution of this complex was used to deposit a Nic-templated molecularly imprinted polymer (MIP-Nic) film on an Au electrode of a quartz crystal resonator of EQCM by potentiodynamic electropolymerization. The imprinting factor was as high as ~9.9. Complexation of the Nic molecules by the MIP cavities was monitored with X-ray photoelectron spectroscopy (XPS), as manifested by a negative shift of the binding energy of the Zn 2p3/2 electron of ZnPc-S16 after Nic templating. For sensing applications, simultaneous chronoamperometry (CA) and piezoelectric microgravimetry (PM) measurements were performed under flow-injection analysis conditions. The limit of detection of the CA and PM chemosensing was as low as 40 and 12 µM, respectively. Among them, the CA chemosensing was more selective to the cotinine and myosmine interferences due to the 1.10 V vs. Ag/AgCl discriminating potential of nicotine electro-oxidation applied. Differences in selectivity to the analyte and interferences were interpreted by modeling complexation of Nic and, separately, each of the interferences with a "frozen" MIP-Nic molecular cavity.