Anliang Zhang

A microreactor using surface acoustic wave as energy source

A microreactor is a key operation unit in a microfluidic device. However, lots of biochemical reactions do not occur at room temperature. Thus, a heating unit in these microfluidic devices is indispensable. A new microreactor with surface acoustic wave (SAW) as an energy source is presented. The microreactor has three elements, including surface acoustic wave heating source, two PDMS micro-vessels and a heat-transfer sheet metal. A glycerin microfluid in the PDMS micro-vessel on the piezoelectric substrate was heated by SAW radiation. The heat was then transferred to the reactants in the PDMS micro-vessel on the sheet metal. The heating effect of the microreactor was verified by melting solid paraffin and color development reaction. The results show that the microreactor can raise the temperature of reactants from 16.1°C of room temperature to higher than 60°C, which is enough for lots of biochemic reactions occurring at about 40°C. The results also show that the microreactor can greatly improve the reaction velocity of starch color development reaction.

Generation of droplets for lab-on-a-piezoelectric-substrate utilizing surface acoustic wave

The generation of droplet is indispensable for micro-fluidic device. A new method for generation of droplet was proposed. An interdigital transducer and reflector were fabricated on a 128°yx-LiNbO3 substrate. A PDMS micro-channel with back taper shape was used to connect a syringe and a needle with sub-micron inside diameter, which was supported by arc PDMS. The tip of the needle was above the piezoelectric substrate with small distance. Fluid was aggregated at the tip of the needle due to the syringe pump. As soon as the fluid was large enough and contacted to the piezoelectric substrate, the fluid was driven by surface acoustic wave and finished the generation of one droplet. Red dye solution was used to generation experiment of droplet. Results show that the volume of generated droplet is decided on the needle radius, the gap between the needle and the piezoelectric substrate and RF signal power. The method of droplet generation is useful for lab-on-a-piezoelectric-substrate for biochemical analysis.

A paper-based microfluidic switch activated by surface acoustic waves

A microfluidic switch is indispensable for a programmable paper-based microfluidic device. A new paper-based microfluidic switch, which could be activated by surface acoustic wave (SAW), was presented. The presented microfluidic switch was consisted of a PDMS micro-shelf and a three-fold paper channel. The PDMS micro-shelf was mounted on a (XY)/128° LiNbO3 substrate, on which a pair of interdigital transducers (IDTs) with 27.5MHz working frequency and two reflectors were fabricated. The folded paper channel was fixed on the PDMS micro-shelf using PDMS micro-wedges. When a RF signal with 27.5MHz frequency was applied to the IDTs, two SAWs were generated. And the microfluid on the piezoelectric substrate was transported to the folded paper channel by SAWs. Then, the folded angles of the folded paper channel were increased so that the folded paper channel could connect with two paper-based microchannels waiting for connection to implement the function ‘on’ of the switch. Red dye solution microfluid has been successfully used to demonstrate the switch function. The work is valuable for a programmable paper-based microfluidic device.

Fast washing micro-reactor on piezoelectric substrate based on surface acoustic wave

Residual contamination in micro-reactor is usually a source of errors for micro-fluidic biochemical analysis system. A new method for fast washing micro-reactor has been proposed. An interdigital transducer with 27.7MHz center frequency and a reflecting gate have been fabricated on 128° YX-LiNbO3 substrate. A micro-reactor is on the propagation path of the piezoelectric substrate. Washing agent is piped on the piezoelectric substrate at first and then actuated to the micro-reactor by surface acoustic wave. As soon as the washing agent arrives at the micro-rector on the piezoelectric substrate, the RF signal power added on the IDT is decreased to ensure that the washing agent is not actuated but can be rotated by small amplitude SAW. Then the contamination in the micro-reactor quickly dissolves with the washing agent due to the small amplitude SAW. At last, the contamination together with the washing agent in the micro-reactor is actuated and washing operation is finished. Dried red dye contamination on micro-reactor was washed by water washing agent, and dried potassium iodide and sodium thiosulfate mixed solution contamination was also washed by water washing agent, which were all by help of SAW. Washing effects were measured by observation or quantitative analysis using gray values. The washing method is great useful for “lab on a piezoelectric substrate” due to without any extra size and cost.

Fast mixing digital micro-fluids in PDMS microchannel based on surface acoustic wave

Mixing liquid in small volumes is a key operation for the development of micro-fluidic devices. In this paper, a new method for fast mixing digital micro-fluids has been developed. Two orthogonal interdigital transducers were fabricated on a 128° YX-axis-rotated cut LiNbO 3 substrate. Each interdigital transducer was 35 straight finger pairs in a simple repeating patter, 4.32mm aperture, and a wavelength of λ=144µm. T-type PDMS micro-channel with 2.5 mm in width and 0.5mm in depth was mounted on the substrate for directing digital micro-fluids. Amplified RF signals were then fed to the IDTs in succession to actuate digital micro fluids along PDMS micro channel. The mixture was characterized using 2µl water-2µl red dye digital micro-fluids and 2µl glycerol-2µl red dye digital micro-fluids. Mixture performances of the digital micro-fluids were accessed by our developed soft. The results show that the mixture velocity and mixture degree of digital micro-fluids in PDMS micro-channels are greatly improved by help of surface acoustic wave than that by free diffusion.

Surface acoustic waves as the energy source for droplet-based micro-reactor with oil encapsulation

A SAW-based micro-reactor for biochemical assay using droplets encapsulated inside oil droplets is reported. Two interdigital transducers (IDTs) with 35 finger pairs, apertures of 4.32mm, and a center frequency of 27.7MHz were fabricated on a 127.86° rotated Y-cut X-propagating LiNbO 3 substrate. Biochemical reagent droplets encapsulated in oil droplets, which the reagent evaporation rate was greatly reduced, were pipetted onto the substrate. SAW generated by the IDTs heated the oil droplets and then raised the temperature of the reagent droplets. A color development reaction of starch has been tested. Gray value of an image has been used to analyze reaction response. Results show that the reaction velocity is accelerated with increased RF signal power fed onto the IDTs. The micro-reactor has the potential to systematically perform economical biochemical analysis on a chip.

Fast mixing of digital droplets under uni-direction acoustic field

A micro-mixer for mixing digital droplets fabricated on 128degY cut X LiNbO3 is reported, which is composed of one interdigital transducers and one reflector for generating unidirectional acoustic field. After a RF signal amplified by a power amplifier was added on an interdigital transducer, surface acoustic wave was excided by the interdigital transducer, and was conversed into longitudinal acoustic wave and to drive a digital droplet to merge with the other droplet quickly by their rapid molecular diffusion when the surface acoustic wave passed through the droplets. Mixing experiments of 3ul NaCl solution-2ul red dye solution and 3ul glycerine-2ul red dye solution show that their mixing velocities can improve 35 folds and 50 folds respectively under unidirectional acoustic fields. The research is valuable for its simplicity in process and easy integration into lab-on-a-chip.