||In the conventional sample extraction approach, to achieve efficient liquid-liquid phase separation for the sample analysis is an important issue. However, it is challenging to separate the immiscible liquid of low surface tension from water by using microfluidic device. Therefore, this study developed a microfluidic chip that composed of T-junction, reaction channel and a novel liquid-liquid phase separator for continuously synthesizing fine gold nanoparticles (AuNPs) in the organic solvent (toluene). The design of glass chip is capable for separating water (surface tension = 72.75 mN/m) and toluene (surface tension = 30.9 mN/m) with 92% separation efficiency, owing to design different depths of microchannel that creates large difference between liquid surface tension and capillary force. Furthermore, AuNPs that synthesized in the microdevice exhibits narrower size distribution and better dispersion in comparing to the typical vessel synthesis process.|
Besides, this study successfully developed a novel and high performance colorimetric probe for dopamine (DA) detection. Aqueous-phase AuNPs extracted via 4-(dimethylamino) pyridine (DMAP) from toluene were used as the reaction probes. Interestingly finding that the original diameter of AuNPs around 13 nm which separated into 2-5 nm size after adding DA. This exhibits change in the color of AuNPs colloid from red to blackish green. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) showed the AuNPs break into the smaller sizes right after addition of DA. The DA concentration is quantitatively monitored by using UV-Vis spectrometer with a limit of detection (LOD) as low as 5 nM. In addition, the developed DA detection approach appears no significant problems in detecting DA with present common interferents such as ascorbic acid (AA), homovanillic acid (HVA) and catechol (CA).
However, many study reported that using microfluidic chip is capable to provide fast chemical reaction and rapid detection approach for biochemical analysis. This study developed a novel optical detection sensor by using the etched multi-mode optical fibers assembling in a droplet-based microfluidic system to achieve on-site absorbance measurement. Hence, the reaction of AuNPs detecting DA biosample was also capable to achieve rapid and continuously detection by using the microdevice. The proposed optical detection sensor composed by initially forming AuNPs droplet in segmented flow and measuring for sample absorbance in a 10 mm long of optical detection channel. Note that using the microdevice for absorbance measurement only required sample volume for 50 nL, which exhibits lower sample consumption in comparing to detect in the conventional cuvette system. Results indicated the developed microdevice capable for steady measuring sample absorbance with operating flow rate in the range from 5-25 μL/min. In addition, the detection approach shows faster reaction response for kinetic measurement of DA core etching AuNPs.
Therefore, this study successfully developed microfluidic chip to provide efficient liquid-liquid phase separation, which benefit to use for the sample extraction and synthesizing AuNPs of uniform size distribution in toluene. In addition, assembling optical fibers on the microfluidic chip that have offers simple and high performance optical detection to the bioanalysis. In this regard, the proposed microdevice with using AuNPs probes shows great potential to achieve high sensitivity detection for the future applying to such as biology, medical and clinic diagnostic applications.