Fast Aptamer Generation Method Based on the Electrodynamic Microfluidic Channel and Evaluation of Aptamer Sensor Performance.

We demonstrate for the first time a fast aptamer generation method based on the screen-printed electrodynamic microfluidic channel device, where a specific aptamer selectively binds to a target protein on channel walls, following recovery and separation. A malaria protein as a model target, Plasmodium vivax lactate dehydrogenase (PvLDH) was covalently bonded to the conductive polymer layer formed on the carbon channel walls to react with the DNA library in a fluid. Then, the AC electric field was symmetrically applied on the channel walls for inducing the specific binding of the target protein to DNA library molecules. In this case, the partitioning efficiency between PvLDH and DNA library in the channel was attained to be 1.67 × 107 with the background of 5.56 × 10-6, which was confirmed using the quantitative polymerase chain reaction (qPCR). The selectively captured DNAs were isolated from the protein and separated in situ to give five aptamers with different sequences by one round cycle. The dissociation constants (Kd) of the selected aptamers were determined employing both electrochemical impedance spectroscopy (EIS) and the fluorescence method. The sensing performance of each aptamer was evaluated for the PvLDH detection after individual immobilization on the screen-printed array electrodes. The most sensitive aptamer revealed a detection limit of 7.8 ± 0.4 fM. The sensor reliability was evaluated by comparing it with other malaria sensors.

Detection of Nitric Oxide from Living Cells Using Polymeric Zinc Organic Framework-Derived Zinc Oxide Composite with Conducting Polymer.

Sensitive and selective detection of nitric oxide (NO) in the human body is crucial since it has the vital roles in the physiological and pathological processes. This study reports a new type of electrochemical NO biosensor based on zinc-dithiooxamide framework derived porous ZnO nanoparticles and polyterthiophene-rGO composite. By taking advantage of the synergetic effect between ZnO and poly(TTBA-rGO) (TTBA = 3'-(p-benzoic acid)-2,2':5',2″-terthiophene, rGO = reduced graphene oxide) nanocomposite layer, the poly(TTBA-rGO)/ZnO sensor probe displays excellent electrocatalytic activity and explores to detect NO released from normal and cancer cell lines. The ZnO is immobilized on a composite layer of poly(TTBA-rGO). The highly porous ZnO offers a high electrolyte accessible surface area and high ion-electron transport rates that efficiently catalyze the NO reduction reaction. Amperometry with the modified electrode displays highly sensitive response and wide dynamic range of 0.019-76 × 10-6 m with the detection limit of 7.7 ± 0.43 × 10-9 m. The sensor probe is demonstrated to detect NO released from living cells by drug stimulation. The proposed sensor provides a powerful platform for the low detection limit that is feasible for real-time analysis of NO in a biological system.

Analysis of Phthalate Esters in Mammalian Cell Culture Using a Microfluidic Channel Coupled with an Electrochemical Sensor.

An analytical tool to monitor trace phthalate was developed using a microfluidic channel device coupled with a novel electrochemical biosensor. At first, the electrochemical sensor was constructed with biomimetic layers to reveal a large hydrogen over potential by controlling the surface charge and hydrophobicity through assembling with a lipid (1,2-dioleoyl-sn-glycero-3-phosphoethanolamine) and a cationic molecule (toluidine blue O) bonded to a conductive polymer. The modified electrode possessing a highly negative polarization potential (approximately -1.8 V vs Ag/AgCl) can uptake sparingly soluble phthalate ester (PEs) compounds in aqueous media. Each sensor probe material was characterized employing SEM, AFM, XPS, QCM, TEM, UV-visible, and impedance spectroscopy. The microfluidic channel is used first to concentrate and separate trace amounts of phthalates, and then the sensor probe is installed at the end of channel. Experimental variables affecting the PEs analysis were assessed and optimized in terms of biomimetic layer composition and analytical conditions. The linear dynamic range and detection limits of the PEs were 0.15 nM-10.0 µM and ∼12.5 pM with relative standard deviations <5%. The proposed method was applied to evaluate the effect of endocrine disruptors on mammalian kidney cells, where the cell samples show in-taking percentages between 1.8 and 7.0% to the total PEs according to the incubation time.