## 1 Introduction  
The focus of cell studies at the single cell level has emerged and expanded to further explore and understand the properties and specific responses of individual cells towards environmental conditions and treatment. Most of the methods available for cell analysis involve experiments performed in an array of culture media and treatments. The responses of single cells to the culture treatments are measured as the average response of a single cell population. Therefore, the heterogeneity of individual cells could be neglected, thus hiding the important signals or responses representing important individual or single cell properties. An individual manipulation platform is needed to perform analysis on a specific single cell. Previous single-cell mechanical and electrical characterization studies have been carried out by probing the single cells using an Atomic Force Microscopy (AFM) probe [1; 2; 3; 4; 5; 6], the micropipette aspiration technique [7; 8; 9], a red blood cell (RBC) biomembrane probe [6; 10; 11], optical tweezers [6; 12; 13; 14], and a microfluidic channel [15; 16; 17; 18; 19] to characterize single cell stiffness, adhesion, and electrical properties. AFM probe, micropipette aspiration, and biomembrane probe techniques require a single cell to be isolated and manipulated manually by a skilled operator using the micromanipulator system. The advancement of microfluidic technology has made single cell capturingpossible by controlling the fluid flow. Additionally, the channels could be utilized as the individual platform for cell manipulations in microscale. A variety of techniques have been employed to trap an individual cell within a microfluidic device. For example, microwell-based [20; 21; 22; 23; 24], dielectrophoresis-based [25; 26; 27; 28; 29], and hydrodynamic-based [30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 41; 42] microfluidic devices for single-cell trapping have been developed in response to an increasing demand for simple yet reliable tools for high-throughput cell manipulation at the single cell level. In microwell-based platforms, a precise geometry design is required to achieve high trapping efficiency [22]. Dielectrophoresis-based cell trapping applied a non-uniform AC field to manipulate polarized particles in suspension and is an effective technique to efficiently manipulate a single cell. However, this technique appears to damage the trapped cells, thus affecting the cell proliferation. Hydrodynamic trapping uses the altered fluidic resistance created by microstructures on a fluid path, such as sieve-like traps [41; 42; 43] or small trapping sites [30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 44; 45], to control the movement of cells in a microchannel. For straight or serpentine-shaped channels with trapping sites, the fluidic resistances of these channels are carefully calculated so that the fluid and cells in the main channel will be directed into the trapping sites when the channels are empty, but bypass them when they are occupied with a cell. The main challenge in hydrodynamic trapping is that it requires a precise microfluidic control of multiple streams and further investigation and optimization of cell trapping efficiencies are still required. Current microfluidic devices used for cell/3D cell culture face some drawbacks that limit their practical usage, such as the difficulty of accessing the trapped cells/3D cells in their trapping sites and the complexity of harvesting the cultured/treated cells for further analysis [46; 47; 48]. In this paper, we develop a T-channel single cell trap to capture a single cell and provide a platform for individual cell characterization. This T-channel provides a trapping site that allows for manipulation of a single cell using the trap channel's outlet port via a syringe pump. Furthermore, the trapping site is not limited to the application of single cell study, but could be used for single 3D cell analysis for drug treatments, single spheroid tumor metastasis investigation, and protein study.