Abstract 400: Immunofluorescence chromatographic assay of tumor cells in dried blood spot
Authors: Zhao Ming , Ma Dakang , Shen Quanxu , Hong Bin 
Published: July 2016

Blood droplet, when desiccated on a surface, forms a ring-like deposit, akin to the coffee ring left after a coffee spill. When blood, coffee, or other aqueous suspensions of the colloidal particles, evaporate with contract line pinned on the underlying hydrophilic surface, a capillary force is generated by the evaporative flux, which drags nearly all the particles to the edge. As the evaporation extends, the volume of the droplet decreases, and the sol-gel transition occurs. The gelation gradually moves inward from the edge to the center, eventually immobilizes all particles, and develops the ring effect. Because smaller sized particles diffuse much more quickly and efficiently than the larger ones, smaller particles tend to preferentially accumulate on the rim, forming multi-layered self-assembly. Contrarily, the majority of the larger particles congregate in the central area. This natural phenomenon simply presents a size-dependent chromatography of variously sized particles in solution. Separation of normal blood cells or break-free tumor cells has been widely utilized for blood disease diagnosis and cancer prognosis. Traditional preparation via blood smear and advanced separation by the external driving forces, e.g. centrifugation and powered microfluidics, could be limited by the technical difficulty, assay complexity, and cell integrity. Coffee-ring based blood cell separation and detection, namely dried spot biopsy, is however a hand-free, cell-harmless, spontaneous process. To perform a dried spot biopsy, 3×1 inch microscope slides were first cleaned to remove surface impurities and residues. 200 uL of freshly collected, anti-coagulated whole blood, bearing fluorescent microbeads (1 and 10 um sized) or pre-stained breast tumor cells (MDA-MB-231, ∼15 um sized), was dispensed onto the slide and allowed to dry statically or acceleratedly on a moving stage at controlled temperature and humidity. Three hydrophilic coatings and five surfactants were examined to balance the outward capillary flow with the inward Marangoni flow for optimal coffee ring effect. It is demonstrated that two sizes of microbeads formed separate rings, a few hundreds of microns in average apart from each other, while tumor cells, acting differently, concentrated in the central area with random dispersion, probably because of the diversified cell sizes. The dried spot biopsy could have a potential for detecting blood borne biomarkers in the form of dried blood specimens that poses longer shelf life, less biohazardous risk, and easier transportation protocol than the liquid form. Additionally, specific cells of interest from microscopic regions of dried blood film can be retrieved by laser microdissection for downstream analyses. Particularly, this method could be valuable for use in low-resourced regions and countries.

Citation Format: Ming Zhao, Dakang Ma, Quanxu Shen, Bin Hong. Immunofluorescence chromatographic assay of tumor cells in dried blood spot. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 400.