Browsing by Author "Saateh, Abtin"

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Open Access
Evaporation-induced biomolecule detection on versatile superhydrophilic patterned surfaces: glucose and DNA assay
(American Chemical Society, 2018) Beyazkilic, Pınar; Saateh, Abtin; Bayındır, Mehmet; Elbuken, Çaglar
We introduce a droplet-based biomolecular detection platform using robust, versatile, and low-cost superhydrophilic patterned superhydrophobic surfaces. Benefitting from confinement and evaporation-induced shrinkage of droplets on wetted patterns, we show enrichment-based biomolecular detection using very low sample volumes. First, we developed a glucose assay using fluorescent polydopamine (PDA) based on enhancement of PDA emission by hydrogen peroxide (H2O2) produced in enzyme-mediated glucose oxidation reaction. Incubation in evaporating droplets resulted in brighter fluorescence compared to that in bulk solutions. Droplet assay was highly sensitive toward increasing glucose concentration while that in milliliter-volume solutions resulted in no fluorescence enhancement at similar time scales. This is due to droplet evaporation that increased the reaction rate by causing enrichment of PDA and glucose/glucose oxidase as well as increased concentration of H2O2 generated in shrinking droplet. Second, we chemically functionalized wetted patterns with single-stranded DNA and developed fluorescence-based DNA detection to demonstrate the adaptability of the patterned surfaces for a different class of assay. We achieved detection of glucose and DNA with concentration down to 130 μM and 200 fM, respectively. Patterned superhydrophobic surfaces with their simple production, sensitive response, and versatility present potential for bioanalysis from low sample volumes. Copyright
Open Access
Real-time impedimetric droplet measurement (iDM)
(Royal Society of Chemistry, 2019) Saateh, Abtin; Kalantarifard, Ali; Çelik, Oğuz Tolga; Asghari, Mohammad; Serhatlıoğlu, Murat; Elbüken, Çağlar
Droplet-based microfluidic systems require a precise control of droplet physical properties; hence, measuring the morphological properties of droplets is critical to obtain high sensitivity analysis. The ability to perform such measurements in real-time is another demand which has not been addressed yet. In this study, we used coplanar electrodes configured in the differential measurement mode for impedimetric measurement of size and velocity. To obtain the size of the droplets, detailed 3D finite element simulations of the system were performed. The interaction of the non-uniform electric field and the droplet was investigated. Electrode geometry optimization steps were described and design guideline rules were laid out. User-friendly software was developed for real-time observation of droplet length and velocity together with in situ statistical analysis results. A comparison between impedimetric and optical measurement tools is given. Finally, to illustrate the benefit of having real-time analysis, iDM was used to synthesize particles with a predefined monodispersity limit and to study the response times of syringe pump and pressure pump driven droplet generation devices. This analysis allows one to evaluate the ‘warm-up’ time for a droplet generator system, after which droplets reach the desired steady-state size required by the application of interest.
Open Access
Real-time impedimetric microfluidic droplet measurement: IDM
(2019-08) Saateh, Abtin
Droplet-based micro uidic systems require a precise control on droplet physical properties, hence measuring the morphological properties of droplets is critical to obtain high sensitivity analysis. The ability to perform such measurements in real-time is another demand which has not been addressed yet. In this study, coplanar electrodes were used, and con gured in di erential measurement mode for impedimetric measurement of size and velocity. To obtain the size of the droplets, detailed 3D nite element simulations of the system were performed. The interaction of the non-uniform electric eld and the droplet was investigated. The electrode geometry optimization steps were described and design guideline rules were laid out. Size of the electrodes was optimized based on the simulations for droplet lengths ranging from 300 to 1500 μm. A user-friendly software was developed for real-time observation of droplet length and velocity together with in-situ statistical analysis results. A detailed comparison between impedimetric and optical measurement tools is given. Finally, to illustrate the bene t of having real-time analysis, iDM was used for experimental studies. First study case is the response time of the syringe pump and pressure pump driven droplet generation devices. This analysis allows one to evaluate the `warm-up' time for a droplet generator system after which droplets reach the desired stead-state size required by the assay of interest. Second, an evaluation chip was designed to investigate e ective factors and their interplay with droplet length variation. A comprehensive design of experiment (DoE) method is utilized. Analyzing the obtained results revealed e ect of each factor and their interactions. Exploiting results of this study contributes to monodisperse micro uidic droplet generation. Monodisperse polymeric particles of polyethylene glycol were synthesized to demonstrate the potentials of monodisperse droplet generation in biochemical synthesis/analysis.