Nusret Ertaş

Multiplex detection and quantification of bacteria in water by using portable devices are particularly essential in low and middle-income countries where access to clean drinking water is limited. Addressing this crucial problem, we report a highly sensitive immunoassay sensor system utilizing the fluorescence technique with magnetic nanoparticles (MNPs) to separate target bacteria and two different types of quantum dots (CdTe and Ni doped CdTe QDs) incorporated into a passive microfluidic chip to transport and to form sandwich complexes for the detection of two target bacteria, namely Escherichia coli (E. coli) and Salmonella enteritidis (S. enteritidis) in less than 60 min. The assay is carried out on a capillary driven microfluidic chip that can be operated by merely pipetting the samples and reagents, and fluorescence measurements are done by using a handheld fluorescence spectrophotometer, which renders the system portable. The linear range of the method was found to be 10¹ to 10⁵ cfu mL⁻¹ for both E. coli and S. enteritidis. The limit of detection (LOD) was calculated to be 5 and 3 cfu mL⁻¹ for E. coli and S. enteritidis, respectively. The selectivity of the method was examined by testing Enterobacter dissolvens (E. dissolvens) and Staphylococcus aureus (S. aureus) samples, and no significant interference was observed. The method was also demonstrated to detect bacteria in tap water and lake water samples spiked with target bacteria.

Quantum dots (QDs) are luminescent semiconductor nanocrystals that have extraordinary luminescence emission properties. Their semiconductor properties are different from bulk material because of the quantum confinement effects. These properties allow the use of QDs as a luminescent probe for pharmaceutical and biomedical analysis. Herein, we want to mention the synthesis, surface modification, characterization, and application of QDs. The aim of this chapter is to compile and discuss the advantages and disadvantages of QDs and their usage areas.

Dispersive liquid–liquid microextraction based on solidification of floating organic drop (DLLME–SFO) was for the first time combined with field‐amplified sample injection (FASI) in CE to determine four β₂‐agonists (cimbuterol, clenbuterol, mabuterol, and mapenterol) in bovine urine. Optimum BGE consisted of 20 mM borate buffer and 0.1 mM SDS. Using salting‐out extraction, β₂‐agonists were extracted into ACN that was then used as the disperser solvent in DLLME–SFO. Optimum DLLME–SFO conditions were: 1.0 mL ACN, 50 μL 1‐undecanol (extraction solvent), total extraction time 1.5 min, no salt addition. Back extraction into an aqueous solution (pH 2.0) facilitated direct injection of β₂‐agonists into CE. Compared to conventional CZE, DLLME–SFO–FASI–CE achieved sensitivity enhancement factors of 41–1046 resulting in LODs in the range of 1.80–37.0 μg L⁻¹. Linear dynamic ranges of 0.15–10.0 mg L⁻¹ for cimbuterol and 15–1000 μg L⁻¹ for the other analytes were obtained with coefficients of determination (R²) ≥ 0.9901 and RSD% ≤5.5 (n = 5). Finally, the applicability of the proposed method was successfully confirmed by determination of the four β₂‐agonists in spiked bovine urine samples and accuracy higher than 96.0% was obtained.

Dispersive liquid–liquid microextraction method based on solidification of floating organic drop (DLLME-SFO) was combined for the first time with counter-electroosmotic flow normal stacking mode (counter-EOF NSM) in capillary electrophoresis (CE) for preconcentration and determination of bisphenol A (BPA) in water and urine samples. Several parameters affecting extraction efficiency, including type and volume of the extraction and disperser solvents, pH, volume of sample and back-extraction solutions, and ionic strength, were systematically studied. In-vial back-extraction of the target analyte from the resulting organic drop into an aqueous phase facilitated the direct application of DLLME-SFO with CE. Under optimum conditions, improvement factors of 1250 (water) and 430 (urine) as compared to conventional capillary zone electrophoresis (CZE) were obtained. Calibration graphs were linear up to 100 µg L⁻¹ with coefficients of determination (R²) ≥ 0.9989 and relative standard deviation (RSD %) ≤ 1.9. Limits of detection (LOD) of 0.8 µg L⁻¹ (water) and 2.5 µg L⁻¹ (urine) were achieved. Because this method required simple and inexpensive devices and very small volumes of nontoxic organic solvents, it is an affordable, efficient, and convenient method for extraction and determination of trace amounts of BPA in water and human urine samples.

Ultrasound-assisted emulsification microextraction and dispersive liquidliquid microextraction were compared for extraction of ephedrine, norephedrine, and pseudoephedrine from human urine samples prior to their determination by capillary electrophoresis. Formation of a microemulsion of the organic extract with an aqueous solution (at pH 3.2) containing 10% methanol facilitated the direct injection of the final extract into the capillary. Influential parameters affecting extraction efficiency were systematically studied and optimized. In order to enhance the sensitivity further, field-amplified sample injection was applied. Under optimum extraction and stacking conditions, enrichment factors of up to 140 and 1750 as compared to conventional capillary zone electrophoresis were obtained resulting in limits of detection of 1233 mu g/L and 1.02.8 mu g/L with dispersive liquidliquid microextraction and ultrasound-assisted emulsification microextraction when combined with field-amplified sample injection. Calibration graphs showed good linearity for urine samples by both methods with coefficients of determination higher than 0.9973 and percent relative standard deviations of the analyses in the range of 3.48.2% for (n = 5). The results showed that the use of ultrasound to assist microextraction provided higher extraction efficiencies than disperser solvents, regarding the hydrophilic nature of the investigated analytes.