Erol Akyilmaz

A nanobiocatalytic whole-cell biosensor based on Pseudomonas aeruginosa immobilized on a multi-walled carbon nanotube (MWCNT)/polyvinyl alcohol (PVA) matrix and modified with gold nanoparticles (AuNPs) was developed for the selective detection of penicillin G. The electrochemical response was monitored using differential pulse voltammetry (DPV) via benzoquinone as a redox mediator. Under optimized conditions pH 7.5, 35 ºC, the biosensor exhibited a well-defined linear response in the range of 100-1000 nM with a competitive detection limit (LOD) of 45.2 nM and a relative standard deviation of 4.41% (n=10). The synergetic incorporation of MWCNTs and AuNPs significantly enhanced electron transfer kinetics across the cellular interface. The biosensor demonstrated excellent selectivity toward penicillin G over structurally related antibiotics and co-existing milk components. Applicability was successfully confirmed in milk and yogurt whey samples, yielding highly satisfactory recovery values. By leveraging the naturally protected endogenous enzymatic machinery of intact cells, the proposed platform offers a robust, cost-effective, and reproducible screening system for rapid monitoring of antibiotic residues in complex food matrices.

A biosensor system based on invertase‐Saccharomyces cerevisiae hybrid system has been developed for the determination of sucrose molecule. For the determination of sucrose in the linear determination range of 0.1–5.0 µM, at 0.5 V potential, the limit of detection (LOD) was found to be 0.08 µM and the limit of quantification (LOQ) was 0.25 µM. With repeatability experiments, the mean value (), standard deviation (±S.D.), and % coefficient of variation (% V.K.) were found to be 1.81 µM, ±0.09 µM, and 4.93%, respectively. Substrate specificity, interference effect, and storage stability were investigated. Sucrose was determined in fruit juice samples.

In this study, for the first time in this field, a biosensor system based on gold nanoparticle/gelatin/glutaraldehyde(AuNP/GE/GA) modified spinach homogenate was developed for the determination of L‐phenylalanine, which can be an alternative and new method in the detection of phenylketonuria disease. For this purpose, in this study, a new biosensor system based on AuNP/GE/GA‐modified spinach homogenate was developed for the rapid, specific, sensitive, and reproducible determination of L‐phenylalanine. With the designed biosensor, measurements were taken in the potential range of (−0.3 to 0.0 V) using the differential pulse voltammetry method in the medium containing tetrahydrobiopterin. The linear range for L‐phenylalanine was determined to be 5–100 µM. With the developed AuNP/GE/GA‐modified spinach homogenate‐ based biosensor, the limit of detection was set at 2.09 µM. Response time was calculated as 10 s. One of the most important and applicable advantages of the developed biosensor was that it enables rapid, selective, repeatable, and sensitive determination without requiring expensive equipment.

The current study develops the first and novel gold nanoparticle‐ionic liquid nanostructure modified microbial biosensor based on Pleurotus ostreatus for the sensitive determination of Bisphenol A. In the construction of the microbial biosensor, lyophilized P.ostreatus cells were modified with ionic liquid‐cysteamine mixture on a gold electrode which was modified with 1,6‐hexanedithiol and gold nanoparticle. The measurement principle of the biosensor is based on the detection of changes in current in a phosphate buffer system (pH 7.5, 50 mM and containing 5.0 mM K₃[Fe(CN)₆]) in the potential range of −0.2 to +0.6 V depending on the BPA concentration. In the optimization studies of the microbial biosensor; the most suitable ionic liquid‐cysteamin ratio was 1 : 2 (v/v) and the incubation time of 1,6‐hexanedithiol on the gold electrode was 6 hours. Optimum working conditions were determined to be pH:7.5, 100 mM potassium phosphate buffer, and 35°C. In the characterization studies of the microbial biosensor, parameters such as linearity, interference effects of some substances on the microbial biosensor responses, repeatability, reproducibility and storage stability of the microbial biosensor were determined. The linear range of the biosensor was obtained 10–250 μM. Limit of detection was determined to be 1.57 μM and the response time was obtained 20 seconds. Real sample analysis was carried out by water samples that kept in plastic bottles for 6 months by using both the microbial biosensor and HPLC method.

Galaktoz seviyesinin ölçümü, galaktozemi ve galaktoz intoleransı açısından klinik önem taşır. Özellikle yenidoğanlarda hemen tespit edilmemesi ölümcül sonuçlar doğurabilir. Teşhis konduktan sonra da galaktozun diyetten çıkarılması gerekir. Dolayısıyla hem kan hem de diyette özellikle süt ve süt ürünlerinde galaktozun tayini büyük önem taşır. Literatür verilerinde galaktoz tayini için geliştirilen yöntemler spektrofotometre, kromatografi, kütle spektrometresi gibi ön işlem ve pahalı ekipman gerektiren, zaman alıcı ve nispeten yavaş yöntemlerdir. Bu çalışmanın amacını da galaktoz tayini için hızlı, spesifik, ucuz elektrokimyasal bir biyosensör sistemi geliştirilmesi oluşturmaktadır. Biyokomponent olarak Galaktoz Oksidaz (GaOX) enzimi kullanılan bu çalışmada, çalışma elektrodu olarak Rutenyum mediyatör kompleksi içeren karbon pasta elektrot kullanılmıştır. GaOX enzimi pasta yapısı içerisinde immobilize edilmiştir. Çalışmanın özgünlüğünü pasta yapısı içerisinde kullanılan Rutenyum mediyatör sisteminin kullanılması oluşturmaktadır. Elektrot yapım aşamaları döngüsel voltammetri (CV) yöntemiyle karakterize edilirken, optimizasyon ve karakterizasyon çalışmaları 0&0.9 V arası DP, ve 0.5 V’ta amperometrik ölçümler yoluyla gerçekleştirilmiştir. Çalışmalarda ayrıca çalışma tamponu içerisinde 1 mM p-benzokinon mediyatör sistemi kullanılmıştır.Optimizasyon çalışmaları sonu optimum pH 6,5, optimum sıcaklık ise 30 oC olarak bulunmuştur. Geliştirilen biyosensörün doğrusal tayin aralığı 0.05 – 1 mM arası bulunurken, tekrarlanabilirliği 0.25 mM galaktoz için ortalama 0.24 mM, standart sapma ± 0.021 ve varyasyon katsayısı (%VK) %8,3 olarak bulunmuştur. Girişim etkisi denemesinde herhangi bir girişim gözlenmemiştir. Örnek denemesi liyofilize serum ve laktozsuz süt örneklerinde yapılmış ve % geri elde hesaplanmıştır. Bu projede kullanılan Rutenyum mediyatör kompleksinin biyosensör yapımında kullanılmasına literatürde çok az rastlanılmış olmakla birlikte bu çalışmayla ilk defa bir galaktoz biyosensöründe ve ilk defa bir karbon pasta elektrotla kullanımı gerçekleştirilmiştir.

A new biosensor based on catalase enzyme immobilized on electrochemically constructed polyaniline (PANI) film modified with glutaraldehyde has been developed for the determination of hydrogen peroxide (H₂O₂) in milk samples. Assembly processes of polyaniline and immobilization of the enzyme were monitored with the help of electrochemical impedance spectroscopy. Amperometric measurements have been performed at cathodic peak (−0.3 V vs. Ag/AgCI) which was attributed to reduction of PANI. Hydrogen peroxide was determined by using amperometric method at −0.3 V. The biosensor responses were correlated linearly with the hydrogen peroxide concentrations between 5.0 × 10⁻⁶ and 1.0 × 10⁻⁴ M by amperometric method. Detection limit of the biosensor is 2.18 × 10⁻⁶ M for H₂O₂. In the optimization studies of the biosensor, some parameters such as optimum pH, temperature, concentration of aniline, amount of enzyme, and number of scans during electropolymerization were investigated.

A new peroxidase biosensor was developed using cysteamine–palladium complex-modified gold electrode. The principle of the measurements is based on monitoring increase in the oxidation potential of palladium complex (at + 0.47 V vs Ag/AgCl) using amperometric detection. In the optimization studies of the biosensor, effects of enzyme amount, palladium complex amount, and duration of SAM formation on biosensor responses were investigated to optimize the bioactive layer. The biosensor has a fast response time of less than 10 s to hydrogen peroxide (H₂O₂), with a linear range of 5.0 × 10^{− 6} to 150 × 10^{− 6} M and a detection limit of 3.38 × 10^{− 6} M.