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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 × 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. [ABSTRACT FROM AUTHOR]

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 × 103 to 3.7 × 108 particles mL−1 with a detection limit of 2.0 × 103 particles mL−1. [ABSTRACT FROM AUTHOR]

Herein, a unique electrochemiluminescence (ECL) sensor combined with a paper electrode was proposed for the detection of phenylalanine (L -Phe) in blood samples. The L -Phe detection was performed by converting L -Phe into ammonia using phenylalanine ammonia-lyase (PAL) enzyme and the ECL signal of Ru(bpy)32+ was produced in combination with ammonia as a co-reactant. In this report, we used AuNP decorated paper electrodes to obtain the ECL signal of Ru-(bpy)32+ in the presence of NH3. The produced ammonia molecules were carried to the working electrode and their contact with the sample was cut off. Since there was no contact between the sample matrix and the electrode, the developed method achieved excellent selectivity. According to experimental data, a linear increase of the ECL signals with the logarithms of varying L -Phe concentrations between 1.5 × 10−2 and 1.211 mM was observed with a correlation coefficient (R2) of 0.9898 and a limit of detection (LOD) of 8.4 × 10−3 mM. The proposed method was efficiently applied for L -Phe detection in reference blood samples and the average recovery was calculated as 96.8%. Furthermore, the HPLC-UV method as a comparison verified that the recovery values provided by the proposed method were acceptable with a similarity of 95.1% for L -Phe detection in a reference blood sample. The results showed that the developed ECL sensor combined with the paper electrode can be considered as a promising unique and powerful technique for a point-of-care diagnosis of PKU. [ABSTRACT FROM AUTHOR]

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 3.90×1011 exosome particles µL-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. [ABSTRACT FROM AUTHOR]

In this study, a paper-based electrochemiluminescence (ECL) sensor was developed for the determination of diltiazem hydrochloride (DTZ-HCl), which is a vasodilator of the calcium channel blocker. Herein, the ability of DTZ to act as a co-reactant for Ru(bpy)32+ in the ECL system was utilized. The pharmaceutical dosage forms were studied to verify the applicability of the developed ECL method. A paper electrode was fabricated by mimicking commercial screen-printed electrodes (SPE) and decorated with gold nanoparticles by using an electrodeposition technique in order to enhance the ECL signals. To generate the excited states of the Ru-(bpy)32+/DTZ-HCl pair, the potential in a range from -0.5 to 1.3 V at a scan rate of 100 mV/s was applied by utilizing cyclic voltammetry (CV) to the gold nanoparticle decorated paper electrode (AuNPs@PE). The ECL signals were recorded using the µStat ECL potentiostat, which is controlled by DropView 8400 Software, concurrently. The coefficient of determination and limit of detection obtained from the standard addition method were found as 0.997 and 0.12 µg/mL, respectively. Furthermore, the usage of conventional SPE electrodes confirmed that the results obtained by the developed method were acceptable with the similarity of 97.2% in terms of average recovery value, for the detection of DTZ-HCl in pharmaceutical dosage forms. This study is a startup method to develop highly selective paper-based ECL sensors in routine drug analysis that is fast and low cost. [ABSTRACT FROM AUTHOR]

Olea europaea L. (Oleaceae) leaves have been used for centuries in folk medicine to treat many degenerative and inflammatory diseases including hypertension, atherosclerosis and cardiovascular disorders. The present study was aimed to quantify the phenolic compounds present in three different extracts of O. europaea leaves, and to demonstrate their protective effects on human umbilical vein endothelial cells against oxidative injury induced by H2O2. Oleuropein, hydroxytyrosol, quercetin, luteolin and rutin in the olive leaf extracts were quantified by using a validated HPLC-UV method. Total phenolic content was determined using the Folin-Ciocalteau assay. The MTT and dichlorofluorescein assays were conducted to measure cytotoxicity and intracellular reactive oxygen species generation, respectively. Oleuropein was the major phenolic component. Each phenolic compound (1.0 and 10.0 µM) and each extract (10.0 µg/mL) significantly (p<0.05) preserved human umbilical vein endothelial cells against H2O2- induced toxicity, but olive leaf extract-1 and luteolin seemed to be more effective in studied concentrations even in the inhibition of cellular reactive oxygen species generation (p<0.05). In addition, a positive correlation was found between reactive oxygen species inhibitory activity and total phenol content versus viability protecting capacity of each olive leaf extracts. These results supply a new validated HPLC method for the effective characterization of olive leaf polyphenolic compounds and support the notion that the polyphenolic components of olive leaves are the efficient cytoprotective agents against H2O2-induced oxidative stress and toxicity in human umbilical vein endothelial cells. [ABSTRACT FROM AUTHOR]

Background/aim: We aimed to develop a rapid method to enumerate Listeria monocytogenes (L. monocytogenes) utilizing magnetic nanoparticle based preconcentration and surface-enhanced Raman spectroscopy measurements. Materials and methods: Biological activities of magnetic Au-nanoparticles have been observed to have the high biocompatibility, and a sample immunosensor model has been designed to use avidin attached Au-nanoparticles for L. monocytogenes detection. Staphylococcus aureus (S. aureus) and Salmonella typhimurium (S. typhimurium) bacteria cultures were chosen for control studies. Antimicrobial activity studies have been done to identify bio-compatibility and bio-characterization of the Au-nanoparticles in our previous study and capturing efficiencies to bacterial surfaces have been also investigated. Results: We constructed the calibration graphs in various population density of L. monocytogenes as 2.2 × 101 to 2.2 × 106 cfu/mL and the capture efficiency was found to be 75%. After the optimization procedures, population density of L. monocytogenes and Raman signal intensity showed a good linear correlation (R2 = 0.991) between 102 to 106 cfu/mL L. monocytogenes. The presented sandwich assay provides low detection limits and limit of quantification as 12 cfu/mL and 37 cfu/mL, respectively. We also compared the experimental results with reference plate-counting methods and the practical utility of the proposed assay is demonstrated using milk samples. Conclusion: It is focused on the enumeration of L. monocytogenes in milk samples and the comparision of results of milk analysis obtained by the proposed SERS method and by plate counting method stay in food agreement. In the present study, all parameters were optimized to select SERS-based immunoassay method for L. monocytogenes bacteria to ensure LOD, selectivity, precision and repeatablity. [ABSTRACT FROM AUTHOR]

In this report, we present a paper membrane-based surface-enhanced Raman scattering (SERS) platform for the determination of blood glucose level using a nitrocellulose membrane as substrate paper, and the microfluidic channel was simply constructed by wax-printing method. The rod-shaped gold nanorod particles were modified with 4-mercaptophenylboronic acid (4-MBA) and 1-decanethiol (1-DT) molecules and used as embedded SERS probe for paper-based microfluidics. The SERS measurement area was simply constructed by dropping gold nanoparticles on nitrocellulose membrane, and the blood sample was dropped on the membrane hydrophilic channel. While the blood cells and proteins were held on nitrocellulose membrane, glucose molecules were moved through the channel toward the SERS measurement area. Scanning electron microscopy (SEM) was used to confirm the effective separation of blood matrix, and total analysis is completed in 5 min. In SERS measurements, the intensity of the band at 1070 cm which is attributed to B-OH vibration decreased depending on the rise in glucose concentration in the blood sample. The glucose concentration was found to be 5.43 ± 0.51 mM in the reference blood sample by using a calibration equation, and the certified value for glucose was 6.17 ± 0.11 mM. The recovery of the glucose in the reference blood sample was about 88 %. According to these results, the developed paper-based microfluidic SERS platform has been found to be suitable for use for the detection of glucose in blood samples without any pretreatment procedure. We believe that paper-based microfluidic systems may provide a wide field of usage for paper-based applications. [ABSTRACT FROM AUTHOR]

In this paper, we proposed two sensitive surface-enhanced Raman spectroscopy assays for the determination of modafinil in urine matrix. In the first assay, modafinil was extracted by solid phase extraction and determined after sandwiching with silver nanoparticles. In the second assay, modafinil was extracted by non-specific interaction with magnetic gold nanoparticles and determined by sandwiching with magnetic gold and silver nanoparticles. The non-specific magnetic extraction does not require any analyte specific agent like antibody, aptamer, or molecularly imprinted polymer, therefore, the cost and complexity of the assay is very low. Both assays are capable for application to urine samples with the detection limits under the minimum required performance limit of modafinil. The assays were validated in terms of accuracy, precision, detection limits, and ranges. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this survey monosodium glutamate (MSG) levels in chicken and beef stock cube samples were determined. A total number of 122 stock cube samples (from brands A, B, C, D) were collected from local markets in Ankara, Turkey. High-performance liquid chromatography with diode array detection (HPLC-DAD) was used for quantitative MSG determination. Mean MSG levels (±SE) in samples of A, B, C and D brands were 14.6 ± 0.2 g kg−1, 11.9 ± 0.3 g kg−1, 9.7 ± 0.1 g kg−1and 7.2 ± 0.1 g kg−1, respectively. Differences between mean levels of brands were significant. Also, mean levels of chicken stock cube samples were lower than in beef stock cubes. Maximum limits for MSG in stock cubes are not specified in the Turkish Food Codex (TFC). Generally the limit for MSG in foods (except some foods) is established as 10 g kg−1(individually or in combination). [ABSTRACT FROM PUBLISHER]

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This present paper describes a new approach to fabricate a new amperometric sensor for the determination of glucose. Polyaniline (PANI) film doped with colloidal gold nanorod particles has been used to immobilize glucose oxidase by glutaraldehyde. The polyaniline/gold nanorod composite structure gave an excellent matrix for enzyme immobilization due to the large specific surface area and higher electroactivity. The composite has been characterized by cyclic voltammetry (CV), scanning electron microscopy (SEM), and surface-enhanced Raman spectroscopy (SERS). The SERS spectrum of the surface-immobilized glucose oxidase and the spectrum of the native enzyme indicate that the main feature of the native structure of glucose oxidase was conserved after being immobilized on the polymer matrix. The amperometric response was measured as a function of concentration of glucose at a potential of 0.6 V versus Ag/AgCl in 0.1 M phosphate buffer at pH 6.4. Linear range of the calibration curve was from 17.6 µM to 1mM with a sensitivity of 13.8 µA·mM-1·cm-2 and a limit of detection (LOD) of 5.8 µM. The apparent Michaelis-Menten constant KM was calculated as 1.0mM and the response time was less than 3 seconds. [ABSTRACT FROM AUTHOR]

Paper-based biosensors are considered simple and cost-efficient sensing platforms for analytical tests and diagnostics. Here, a paper-based electrochemical biosensor was developed for the rapid and sensitive detection of microRNAs (miRNA-155 and miRNA-21) related to early diagnosis of lung cancer. Hydrophobic barriers to creating electrode areas were manufactured by wax printing, whereas a three-electrode system was fabricated by a simple stencil approach. A carbon-based working electrode was modified using either reduced graphene oxide or molybdenum disulfide nanosheets modified with gold nanoparticle (AuNPs/RGO, AuNPs/MoS2) hybrid structures. The resulting paper-based biosensors offered sensitive detection of miRNA-155 and miRNA-21 by differential pulse voltammetry (DPV) in only 5.0 µL sample. The duration in our assay from the point of electrode modification to the final detection of miRNA was completed within only 35 min. The detection limits for miRNA-21 and miRNA-155 were found to be 12.0 and 25.7 nM for AuNPs/RGO and 51.6 and 59.6 nM for AuNPs/MoS2 sensors in the case of perfectly matched probe-target hybrids. These biosensors were found to be selective enough to distinguish the target miRNA in the presence of single-base mismatch miRNA or noncomplementary miRNA sequences. [ABSTRACT FROM AUTHOR]