【作者】 董良威；

【导师】 胡越黎；

【作者基本信息】 上海大学 ， 控制理论与控制工程， 2019， 博士

【摘要】 数字流体(液滴)是微流分析系统中的重要操控对象,用于装载或包封DNA分子、蛋白质、细胞、病毒、毒品、生物微粒等生化分析目标物,是生化技术中微反应器,即生化反应的场所。数字微流体(液滴)破裂不仅可以将尺寸较大液滴破裂为尺寸较小微液滴,而且可以实现液滴内溶液浓度控制,在DNA分析、蛋白质分析、细胞分析、毒品检测及生物微粒富集、目标生物微粒分选等得到应用。压电器件由于工艺成熟、简单,微流操作能力强等特点,应用于微流分析系统中,并得到快速发展,因此,压电基片上微流分析系统已经成为微流控学中重要分支,受到国内外学者的高度重视。压电基片上液滴破裂是压电微流分析系统中重要的基础操作,但传统的连续电信号作用于叉指换能器,激发强声表面波使液滴飞逸实现微液滴破裂方法需要较大的电信号功率,限制了其在压电微流分析系统中应用,有待改进。此外,微通道内液滴破裂后也存在子夜滴体积比不能灵活调节的问题。本文针对以上问题,提出了压电基片上微通道内微液滴和开放平面压电基片上液滴破裂方法,并设计了三种基于声表面波微液滴破裂器件。所开展的工作和取得的成果主要体现在以下三个方面:1针对微流器件中微通道内微液滴破裂时子液滴体积比调节较为困难问题,提出了声表面波结合微通道内PVC薄片分叉子通道,实现压电基片上微通道内液滴破裂后子液滴的体积比灵活可调,即体积比可控破裂器。详细设计了压电器件上叉指换能器的参数,并采用微电子工艺在128°YX-LiNbO3压电基片上光刻叉指换能器,将模铸法制作的微通道(PDMS)及PVC分叉的子通道贴合于压电基片上,构建了压电基片上微流体破裂器件。在叉指换能器上施加电信号,其激发的声表面波调节待破裂微液滴在微通道宽度方向上位置,当液滴在油相流体携带下流过PVC薄片,将液滴破裂为两个子液滴。为阻碍破裂后子液滴再度融合,在分叉通道一侧设计阻流条,使得破裂后子液滴在两子通道内流速不一致。以石蜡油为连续相,红墨水溶液微液滴为离散相进行液滴破裂实验,成功地实现了声表面波作用下破裂后子液滴体积比为0.92和1.43。2为克服传统的连续声表面波破裂压电基片上微液滴需要电信号功率较大的缺点,提出了瞬间降低电信号功率方法破裂压电基片上微液滴,提出了微功耗破裂器件。在128°YX-LiNbO3压电基片上光刻中心频率为27.5 MHz叉指换能器,在叉指换能器上施加一定功率的电信号,压电基片上微液滴在声表面波作用下发生形变,瞬间降低该电信号功率,液滴下部由于重力和基片间表面张力作用保持原状态,液滴上部由于声表面波流力的惯性作用逸出液滴而发生破裂。研究了液滴破裂的动力学特性;以红墨水溶液微液滴为实验对象,验证了所提出液滴破裂方法的正确性,当电信号功率从12.3 dBm瞬间降低到-3.98 dBm,4 μl液滴可连续多次发生破裂。3复杂的生化分析系统往往需要质荷多基片间精确输运,提出了压电基片上球珠辅助实现液滴破裂方法,在垂向输运高度精确可控同时实现液滴破裂。在128°YX-LiNbO3压电基片上光刻叉指换能器,其上施加电信号,激发的声表面波驱动液滴沿球珠表面输运,到达球珠顶部后,在足够的声表面波流力下,顶部液滴发生破裂,实现基片空间垂向输运。对液滴受力特性进行分析,并研究了液滴空间输运的力学条件;推导了液滴球珠表面输运的临界体积。实验验证了5μl红色墨水溶液微液滴在30.8 dBm的电信号作用下可以沿2 mm直径的球珠表面输运并成功破裂。另外,作为所提出的基于声表面波液滴破裂方法的应用,将自行研制的声表面波液滴破裂器件应用于不同性质微液滴物理混合及化学显色反应。更多还原

【Abstract】 Digital microfluids(droplets)are important manipulating objects in microfluidic systems because they are not only the carriers like containers loading or encapsulating(bio)chemical reactants such as DNA,porteins,cells,viruses,drugs or bioparticles etc,but also the microreactors where the biochemical reactions take place.The breakup of digital microfluids(droplets)is used not only for controlling the size of the droplets,but also for adjusting the droplet concentration.This technology is widely applied to DNA analysis,portein analysis,cell analysis,drug discover,bioparticle concentration and objective bioparticles separation.Piezoelectric devices are widely applied to microfluidic systems due to their simple technology and strong microfluidic operations ability.A microfluidic system on a piezoelectric substrate is an important branch of the microfluidic analysis system,and is paied attention to by scientists on microfluidic analysis.The breakup of droplets on the piezoelectric substrate is nessary operation for microfluidic system on the piezoelectric substrate.However,traditional method for splitting droplets needs to be imporved due to larger power of an electric signal applied to the interdigital transducer(IDT),which limits its application.Moreover,it is also difficult to adjust the volume ratio of split daughter droplets in the channels of present microfluidic systems.Here,the breakup methods for spliting droplets in channels or on the piezoelectric substrate have been presented,and three types of microfluidic devices have been designed and fabricated.The research results and main contributions of this dissertation are as follows:Firstly,a microfluidie deviee driven by surface acoustic wave on a piezoelectric substrate with a channel divided by a PVC thin slice is fabricated to solve the problem by adjusting volume ratio of split daughter droplets,which is referred as volume ratio controlled breakup device.An IDT is designed,and fabricated on 128°YX-LiNbO3 piezoelectric substrate using microelectronic technology.A polydimethylsiloxane(PDMS)channel is made by die casting,which is divided into two daughter channels by the PVC thin slice.The channel is mounted on the piezoelectric substrate.The position of the droplet to be split is adjusted by surface acoustic wave excited by the IDT.As soon as the droplet in continuous oil phase passes through the PVC thin slice,the droplet is split into two daughter droplets.A small PDMS choke plug is designed in one of the daughter channels for keeping the daughter droplets from re-fusion.Breakup experiments are carried out using red ink solution droplets in continuous paraffin oil phase.Results show that the volume ratios of the split daughter droplets are 0.92 and 1.43 at different power level SAW.Secondly,a new method of droplet breakup by suddenly decreasing the electric signal power is presented to solve the larger power of the electric signal owing to continuous SAW used in traditional droplet splitting,and thus the micropower breakup device is proposed.An interdigital transducer with 27.5 MHz center frequency is fabricated on a 128°YX-LiNbO3 piezoelectric substrate using microelectronic technology.The droplet on the piezoelectirc substrate will be deformated due to acoustic radiation force when an electric signal with certain power applied to the IDT.However,when acoustic streaming force suddenly disappears by moving away the electric signal,the upper part of the droplet will run away from the droplet due to the inertia.The lower part of the droplet keeps the original state by its gravity and surface tension.The dynamical property of the droplet is then analyzed.Red dye solution droplets are demonstrated as the experimental sample to verify the breakup.Results show that a 4μl droplet can be split several times when the electric signal power is suddenly decreased from 12.3 dBm to-3.98 dBm.Finally,a new method of splitting droplet on a piezoelectric substrate with precisely controlled vertical transportation height by help of a small ball is presented to satisfy mass charge tansportation among several substrates in complex biochemical analysis systems.Therefore,a vetical transportation breakup device is proposed.An interdigial transducer is fabricated on a 128°YX-LiNbO3 piezoelectric substrate using microelectronic technology.The droplet is driven and transported along the surface of the small ball by surface acoustic wave.A part of droplet on the top of the ball flies off at the condition of enough electric signal power.The mechanical porperty of the droplet is also described,and force conditions for vertically spatial transportion are given.The critical volume for successful transportion along the ball surface is deduced.A 5 μl red ink solution droplet is successfully transported along the surface of the small ball with 2 mm diameter and then split at 30.8 dBm electric signal power.As applications,the physical mixture of two different droplets and color development reaction are sucessfully implemented in the homemade devices for splitting droplets.更多还原