Circulating tumor cells (CTCs), a type of cancer cell that spreads from primary tumors into human peripheral blood and are considered as a new biomarker of cancer liquid biopsy. variety of approaches have now emerged for CTC isolation and analysis on microfluidic platforms combined with nanotechnology. These new approaches show advantages in terms of cell capture efficiency, purity, detection sensitivity and specificity. This review focuses on recent progress in the field of nanotechnology-assisted microfluidics for CTC isolation and detection. Firstly, CTC isolation approaches using nanomaterial-based microfluidic devices are summarized and discussed. The different strategies for CTC release from the devices are specifically layed out. In addition, existing nanotechnology-assisted methods for CTC downstream analysis are summarized. Some perspectives are discussed on the challenges of current methods for CTC studies and promising research directions. strong class=”kwd-title” Keywords: nanotechnology, circulating tumor cells (CTCs), microfluidic, cell capture, BIBW2992 (Afatinib) cell release, cell analysis 1. Introduction Cancer has become one of the leading causes of death worldwide, and tumor metastasis is the main cause of high cancer mortality . The metastatic process occurs via the transport of malignant tumor cells. Circulating tumor cells (CTCs) are cancer cells that spread through the blood from the primary tumor site . Compared with traditional methods for clinical tumor detection, such as imaging diagnosis, endoscopy and pathological diagnosis, etc., CTC detection has the advantages of noninvasive and dynamic monitoring [3,4]. CTCs are one of the few new tumor molecular markers in cancer diagnosis LPL antibody and therapy assessment and they have been attracting great attention in recent decades. At present, with the expanded understanding of CTCs, their application has moved from the number to the era of molecular typing and cell sequencing [5,6]. The premise of CTC detection is to obtain CTCs from clinical samples. CTCs are extremely rare, with only 1C10 appearing in 1 mL peripheral blood with around 500 million normal blood cells, so isolating and detecting CTCs from the complex and heterogeneous mixtures is a critical task . To date, with the development of micro-electro-mechanical system (MEMS) and micro-total analysis system (TAS) technologies, various microfluidic platforms featured with chambers, channels and nanostructures have promoted the development of CTC research with the ongoing advances of micro/nanotechnologies. Microfluidic systems have the advantages of small sample volume demands, fast processing times, multiplexing capabilities and large surface-to-volume ratios [8,9,10]. These features offer new opportunities for in vitro cell capture and detection. Hence, it is necessary to perform advanced microfluidic-based approaches to realize the efficient capture and release of rare CTCs for clinical cancer studies and applications. In recent years, based on the different biophysical and biochemical characteristics of CTCs, the capture methods of CTCs have generally been divided into physical property-based methods (i.e., size, density, adhesion, deformability, dielectric properties, magnetic susceptibility and hydrodynamic properties, etc. [11,12,13,14]) and affinity reaction-based methods (i.e., antibody, aptamer, etc. [15,16]). Many reviews of the different kinds of CTC capture methods have been reported and many platforms have successfully established the detection BIBW2992 (Afatinib) of CTCs with competitive efficiency and sensitivity [11,15,16,17,18,19,20]. The main advantages of physical property-based capture include the fact that it BIBW2992 (Afatinib) is label-free, simple and fast. For example, microfilters, inertial microfluidics and deterministic BIBW2992 (Afatinib) lateral displacement (DLD) [21,22,23,24,25] are typical passive label-free approaches to size-based CTC isolation. There are several limitations of using fluid dynamics methods, mainly due to the low throughput, clogging issues and bulky experimental setup. In addition, acoustophoresis , dielectrophoresis , magnetophoresis  and optical techniques  have been used for enhanced active CTC isolation and analysis based on the differences in mechanical properties. Compared to passive methods such as DLD and microfilters, active methods based on the mechanical properties BIBW2992 (Afatinib) of CTCs have better flexibility and can achieve superior separation resolution. However, such methods lack specificity and are prone to losing tumor cells other than the characteristic parameters. CTCs also exhibit some unique biochemical properties attributed to the specific tumor markers expressed by CTCs,.
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