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The molecular engineering of conjugated systems has proven to be an effective method for understanding structure-property relationships toward the advancement of optoelectronic properties and biosensing characteristics. Herein, a series of three thieno[3,4-c]pyrrole-4,6-dione (TPD)-based conjugated monomers, modified with electron-rich selenophene, 3,4-ethylenedioxythiophene (EDOT), or both building blocks (Se-TPD, EDOT-TPD, and EDOT-Se-TPD), were synthesized using Stille cross-coupling and electrochemically polymerized, and their electrochromic properties and applications in a glucose biosensing platform were explored. The influence of structural modification on electrochemical, electronic, optical, and biosensing properties was systematically investigated. The results showed that the cyclic voltammograms of EDOT-containing materials displayed a high charge capacity over a wide range of scan rates representing a quick charge propagation, making them appropriate materials for high-performance supercapacitor devices. UV-Vis studies revealed that EDOT-based materials presented wide-range absorptions, and thus low optical band gaps. These two EDOT-modified materials also exhibited superior optical contrasts and fast switching times, and further displayed multi-color properties in their neutral and fully oxidized states, enabling them to be promising materials for constructing advanced electrochromic devices. In the context of biosensing applications, a selenophene-containing polymer showed markedly lower performance, specifically in signal intensity and stability, which was attributed to the improper localization of biomolecules on the polymer surface. Overall, we demonstrated that relatively small changes in the structure had a significant impact on both optoelectronic and biosensing properties for TPD-based donor-acceptor polymers.

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Oxaliplatin (OXP) is a platinum-based chemotherapeutic agent that induces DNA damage by forming intra- and interstrand crosslinks, mainly at the N7s of adenine (A) and guanine (G) bases. In addition to double-stranded DNA, G-rich G-quadruplex (G4)-forming sequences can also be targeted by OXP. However, high doses of OXP can lead to drug resistance and cause serious adverse effects during treatment. To better understand the targeting of G4 structures by OXP, their interactions as well as the molecular mechanisms underlying OXP resistance and adverse effects, there is a need for a rapid, quantitative, and cost-effective method to detect OXP and the damage it causes. In this study, we successfully fabricated a graphite electrode biosensor modified with gold nanoparticles (AuNPs) to investigate the interactions between OXP and the G4-forming promoter region (Pu22) of Vascular endothelial growth factor (VEGF). The overexpression of VEGF is known to be associated with tumor progression and the stabilization of VEGF G4 by small molecules is shown to suppresses VEGF transcription in different cancer cell lines. Differential pulse voltammetry (DPV) was used to investigate the interactions between OXP and Pu22-G4 DNA by monitoring the decrease in the oxidation signal of guanine with increasing OXP concentration. Under the optimized conditions (37 °C, 1:2 v/v AuNPs/water as electrode surface modifier, and 180 min incubation time) the developed probe showed a linear dynamic range of 1.0-10.0 µM with a detection limit of 0.88 µM and limit of quantification of 2.92 µM. Fluorescence spectroscopy was also used to support the electrochemical studies. We observed a decrease in the fluorescence emission of Thioflavin T in the presence of Pu22 upon addition of OXP. To our knowledge, this is the first electrochemical sensor developed to study OXP-induced damage to G4 DNA structures. Our findings provide new insights into the interactions between VEGF G4 and OXP, which could aid in targeting VEGF G4 structures and the development of new strategies to overcome OXP resistance.

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Since conjugated polymers are an important class of materials with remarkable properties in biosensor applications, in this study, a novel glucose biosensor based on a conjugated polymer was fabricated via the electropolymerization of the monomer 10,13-bis(4-hexylthiophen-2-yl)dipyridol[3,2-a:2',3'-c]phenazine onto a graphite electrode surface. Glucose oxidase (GOx) was used as the model biological recognition element. As a result of the enzymatic reaction between GOx and glucose, the glucose amount was determined by monitoring the change in the oxygen level associated with substrate concentration via the amperometric detection technique. The proposed system possessed superior properties with KMapp value of 0.262 mM, 2.88 × 10-3 mM limit of detection and 105.12 µA mM-1 cm-2 sensitivity. These results show that conjugated polymer film provides an effective and stable immobilization matrix for the enzyme. Finally, the biosensor was applied successfully to several commercially available beverage samples for glucose determination proving an inexpensive and highly sensitive system applicable for real time analyses.

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A simple and efficient approach for the preparation of a biosensing platform was developed based on newly designed peptide-SNS type monomer conjugates. The approach involves the electrochemical polymerization of the peptide-SNS type monomer on the electrode surface. To synthesize the peptide bearing monomers, the SNS-type monomer having a carboxylic acid functional group was anchored to the C-terminal of the peptide by solid phase peptide synthesis via coupling reagents. Utilization of peptides to increase the solubility of the monomers was first investigated in this report. The obtained monomers, soluble in water, were fully characterized by spectral analyses and utilized as matrices for biomolecule attachment. Polymerization of monomers in water has the potential to provide an alternative process for the electrochemical preparation of the polymers in aqueous media, without using any organic solvent. Under the optimized conditions, the biosensor responded to the target analyte, glucose, in a strikingly selective and sensitive manner, and showed promising feasibility for the quantitative analysis of glucose in beverages.

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We have developed a hole-blocking layer for bulk-heterojunction solar cells based on cross-linked polyethylenimine (PEI). We tested five different ether-based cross-linkers and found that all of them give comparable solar cell efficiencies. The initial idea that a cross-linked layer is more solvent resistant compared to a pristine PEI layer could not be confirmed. With and without cross-linking, the PEI layer sticks very well to the surface of the indium-tin-oxide electrode and cannot be removed by solvents used to process PEI or common organic semiconductors. The cross-linked PEI hole-blocking layer functions for multiple donor-acceptor blends. We found that using cross-linkers improves the reproducibility of the device fabrication process.

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A conducting polymer modified with sepiolite was utilized in the construction of a highly sensitive and fast amperometric cholesterol biosensor. In this study a monomer; (10,13-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)dibenzo[a,c]phenazine (PHED)) was synthesized and then its polymer was coated on a graphite electrode by electropolymerization to obtain a matrix for enzyme immobilization. Cholesterol oxidase was immobilized onto polymer coated electrode by adsorption technique. Sepiolite was introduced for a successful immobilization of the cholesterol oxidase. Immobilized enzyme kinetic parameters (KM(app), Imax) were evaluated by Michaelis-Menten kinetics and calculated as 0.031 mM and 6.06 µA, respectively. LOD and sensitivity were estimated as 0.36 µM and 1.64 mA/mMcm(2). Characterization of designed biosensor was done to examine the effect of various factors such as enzyme amount, optimum pH and shelf-life. A novel accurate and inexpensive cholesterol biosensor was developed for the determination of total cholesterol in food samples.

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A method for the extraction and selective determination of cations is proposed using electro-synthesized overoxidized sulfonated polypyrrole film. The polymer film is used for the selective extraction of trace levels of nickel and cadmium ions by solid-phase microextraction (SPME). The cation uptake and release properties of the overoxidized sulfonated polypyrrole film electrode were examined under both open circuit and controlled potential conditions for prospective applications in electrochemically controlled solid-phase microextraction. Increased extraction efficiency and selectivity toward cations were achieved in high saline content of water. Simple preparation of film coatings on a platinum wire was possible using a constant potential method. Applied positive and negative potentials facilitated the extraction and desorption of cations, respectively. Nickel and cadmium ions were desorbed into sample aliquot and determined by electrothermal atomic absorption spectrometry (ETAAS). The cation uptake and release mechanism is affected both by the cation exchange at the negative sulfonate and carboxylate moiety on the film and the altered solution pH occurring at the counter electrode caused by the applied potential. The method was validated using a standard reference material and tested for the determination of cadmium ion in commercial table salt samples.