SHAPE-CONTROLLABLE SYNTHESIS OF HYBRID STRUCTURES BY THREE-DIMENSIONAL (3D) HYDRODYNAMIC FOCUSING METHOD Mengqian Lu 1 , Qingzhen Hao 1 , Ahmad Ahsan Nawaz 1 , Lin Wang 2 , Tony Jun Huang 1 1 The Pennsylvania State University, USA, 2 Ascent Bio-Nano Technologies Inc., USA ABSTRACT We synthesized tetrathiafulvalene-Au (TTF-Au) materials by using three dimentional (3D) hydrodynamic focusing (HF) method. The 3D HF was achieved in a single-layer microfluidic device using a novel technique called “microfluidic drifting”. While keeping the flow rate ratio of the reagents as constant but changing the flow rates, the products showed different morphologies. Narrower size distribution was shown compared to the products prepared by vortex mixing. KEYWORDS Microfluidic, Three-dimensional Hydrodynamic focusing, Shape-Controllable Synthesis INTRODUCTION Nano and micro- structures synthesis has attracted increasing interest because of the widely application in various areas, such as biotechnology, medicine, optics, electronics, and so on. [1] Materials synthesis by using microfluidic method has shown its advantages such as reproducibility and high yields. [2] To further improve the monodispersity of products, uniform mechanical, chemical conditions, and reaction time are needed. This requires efficient mixing and uniform flow velocity in the reaction region. Two dimensional (2D) hydrodynamic focusing (HF) has been utilized to improve mixing efficiency and provide a horizontally uniform environment in the reaction region. [3] However, the variability of the flow velocity and chemical conditions in the vertical dimension increase the heterogeneity of the products. Besides, the physical contact of the synthesized particles with the channel wall will result in cross contamination and clogging of the devices. The 3D HF method confines the reaction region to a small volume at the center of the channel. Therefore, it provides uniform chemical and mechanical conditions in both the horizontal and vertical dimensions. In our earlier work, we introduced a novel technique to manipulate fluid called “microfluidic drifting” to achieve 3D HF in a simple single-layer microfluidic device. [4,5] By using this device, we synthesized TTF-Au materials of different morphologies. Similar products of this reaction can be fabricated via bulk mixing while changing the ratio between the two reagents; however, this results in a broader size distribution. EXPERIMENT Two reagents, 1 mM tetrathiafulvalene (TTF) and 0.27 mM hydrogen tetrachloroaurate (HAuCl 4 ) in acetonitrile (ACN) were injected by syringe pumps via the two main inlets. At the sides, ACN was injected as buffer, as shown in Fig. 1a. Table 1. shows the flow rates used in each experiment. The 3D HF was accomplished in a two-step sequence. Firstly, reagent 1 was focused in the vertical direction by using the “microfluidic drifting” technique. At this step, due to a pair of counter-rotating vortices (Dean vortices) caused by the centrifugal effect in the 90-degree curve of the microfluidic channel, reagent 1 was shifted lateral to the middle plane of the channel. Then two horizontal focusing sheath flows (ACN buffer) further compressed reagents flow from both sides. Therefore, 3D HF is achieved with the combination of both steps and reagent 1 can be focused in the center of the microfluidic channel. [4] The simulation of the 3D architecture of reagent 1 was carried out by using the computational fluid dynamic (CFD) simulation (CFDACE+, ESI-CFD), and the result is shown in Fig. 1. From sample a) to sample e), reagent 1 was focused in the center of the channel. For sample f), the flow pattern was different from other samples, but reagent 1 was still confined to a small region. Since the reaction only happens at the interface of the two reagents, the reaction region was confined with uniform chemical and mechanical conditions in both vertical and horizontal directions. Finally, the collected solution was concentrated using a centrifuge and dried on a clean silicon wafer for field emission scanning electron microscopy (FESEM) imaging. Figure 1. The CFD simulation of the 3D architecture of reagent 1 with the flow conditions in Table. 1. 16th International Conference on Miniaturized Systems for Chemistry and Life Sciences October 28 - November 1, 2012, Okinawa, Japan 978-0-9798064-5-2/μTAS 2012/$20©12CBMS-0001 145