Browsing by Author "Tamer, U"

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    Calibration Curve Approaches for Nonlinear Data Points Obtained in Colo 320 Exosomes Determination
    Sazaklioglu, SA; Torul, H; Kabadayi, H; Vatansever, HS; Tamer, U; Celikkan, H
    The limit of detection (LOD) is defined as the lowest quantity or concentration of a component that can be reliably distinguished from the limit of blank (LOB). LOD value is one of the most important parameters considered for many determination methods and is usually calculated on the linear correlation between signal and concentration. However, the linear correlation may not always be obtained in experimental studies. We claim that data with low linear correlation have meaning, and we present such a study because analytical studies based on these data are not easily understood in the literature. In this manuscript, we suggest that a calibration curve can be obtained from nonlinear data points and the LOD value can be calculated. We tested this approach for the determination of exosomes and supported it with mathematical calculations. We produced a label-free sensor using anti-CD63 on the gold electrode for selective and reliable impedimetric detection of the exosomes obtained from Colo 320 cell lines in data points that are high concentrations and out of linearity. We characterized in detail what each calculation means. This sensor with a LOD value of 3.90x1011 exosome particles mu L-1 and with a cubic polynomial model for the calibration curve was considered sensitive and reliable, especially for high vesicle content of samples such as cell culture medium.
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    Direct impedimetric detection of exosomes and practical application in urine
    Sazaklioglu, SA; Torul, H; Vatansever, HS; Tamer, U; Çelikkan, H
    Exosomes are nanoscale vesicles released from tumor-derived cells. They are very popular cancer biomarkers in non-invasive liquid biopsy diagnosis and evaluation of therapeutic response. Rapid analysis of exosomes with proteins or other biomarkers requires complex methods and has a relatively high cost. We indicate the fabrication of a biosensor for the detection of exosomes at low concentrations using immunological recognition strategies. The implementation of the biosensor consists of two steps: (i) functionalization of screen-printed electrodes (SPEs) with tetraspanin anti-CD63 antibodies and (ii) capturing exosomes by the electrode surface. Label-free detection of exosomes was successful with the Nyquist diagram, one of the main demonstrations of electrochemical impedance spectroscopy (EIS). In addition, we increased the consistency of the results by including the Bode diagrams of the measurements in our study. The proposed biosensor as a sensitive and reliable impedimetric method for detecting exosomes was established in a working range of 3.7 x 10( )3 to 3.7 x 10(8) particles mL(-1) with a detection limit of 2.0 x 10(3) particles mL(-1). [GRAPHICS] .
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    Sensitive and reliable lab-on-paper biosensor for label-free detection of exosomes by electrochemical impedance spectroscopy
    Sazaklioglu, SA; Torul, H; Tamer, U; Ensarioglu, HK; Vatansever, HS; Gumus, BH; Çelikkan, H
    A new, sensitive, and cost-effective lab-on-paper-based immunosensor was designed based on electrochemical impedance spectroscopy (EIS) for the detection of exosomes. EIS was selected as the determination method since there was a surface blockage in electron transfer by binding the exosomes to the transducer. Briefly, the carbon working electrode (WE) on the paper electrode (PE) was modified with gold particles (AuPs@PE) and then conjugated with anti-CD9 (Anti-CD9/AuPs@PE) for the detection of exosomes. Variables involved in the biosensor design were optimized with the univariate mode. The developed method presents the limit of detection of 8.7 x 102 exosomes mL-1, which is lower than that of many other available methods under the best conditions. The biosensor was also tested with urine samples from cancer patients with high recoveries. Due to this a unique, low-cost, biodegradable technology is presented that can directly measure exosomes without labeling them for early cancer or metastasis detection.
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    Electrochemically generated paper SERS substrate for detection of exosome in urine samples
    Kayis, EÇ; Torul, H; Sazaklioglu, SA; Çelikkan, H; Ensarioglu, HK; Gumus, BH; Vatansever, HS; Tamer, U
    Here, a single-drop paper-based surface-enhanced Raman spectroscopy (SERS) immunoassay was developed to pave the way for monitoring exosome numbers for the early diagnosis of prostate cancer. Exosomes are nanosized (40-150 nm) membrane vesicles that provide intercellular communication. In our work, we offer a new paper SERS substrate for exosome detection in urine. We initially electrochemically deposited nanostar-shaped gold nanoparticles (AuNPs) on the working electrode to crate the paper SERS substrates. Then we functionalized them with 11-mercaptoundecanoic acid (11-MUA) and conjugated them with anti-CD9 antibodies. After capturing exosomes, the sandwich immunoassay structure was created by using gold nanorods (AuNRs) modified with 5,5-dithiobis (2-nitrobenzoic acid) (DTNB) as a Raman tag. The SERS signal intensities of DTNB molecules at 1330 cm-1 were monitored to determine the exosome concentration. Each step occurred in only one drop of solution or sample. The developed single-drop paper-based SERS immunoassay exhibited a linear range from 1.0 x 103 to 1.0 x 109 exosome particles/mL with correlation coefficients (R2) of 0.9903. The limit of detection (LOD) was found as 9.9 x 101 exosome particles/mL. The developed system was tested with clinical urine samples from patients with benign prostatic hyperplasia, prostatitis, prostate cancer, and healthy individuals. The obtained results were compared with the exosome particle numbers in these samples determined by an enzyme-linked immunosorbent assay (ELISA) method and the accuracy of the system was evaluated with an average recovery value of 96.7 %. The developed biosensor system enables highly sensitive detection of exosomes in low-volume urine samples. The usage of a paper membrane as a SERS substrate, combined with the electrochemical deposition of gold nanoparticles, provides an eco-friendly and cost-effective solution, enabling wider use and applications.