(228du) High Throughput Cell Screening Via Luminescent Nanoparticles in a Microfluidic Device

With the understanding that the molecular backbone of genetic diseases and cancers is the result of lower than expected success rates, the need to screen and tailor treatments to each patient is becoming more vital. Droplet microfluidic devices have garnered significant interest in recent years due to their ability to encapsulate single cells in aqueous droplets for high throughput screening. Recent innovations with droplet microfluidics have included the addition of downstream trapping arrays to collect the aqueous droplets and perform dynamic analysis on intracellular enzyme activity and the cellular response to therapeutics. While these trapping arrays can assess a heterogeneous population of cells, they are currently limited in their ability to test multiple inputs (e.g., different doses or combinations of chemotherapeutics) in a single device. Therefore, it is important to develop this droplet â??barcodingâ?? screening technique that allows for the simultaneous measurement of multiple inputs across a heterogeneous population of cells to perform high throughput, personalized diagnostics. In this work, upconversion luminescence nanostructures are incorporated into a droplet microfluidic trapping array to barcode individual droplets as a means of performing real-time, dynamic analysis of the cellular response in single cells to different treatment protocols.

Specifically, this work focuses on the viability of cells in the presence of the upconversion nanoparticles, NaYF₄ core-shell particles. The rare earth emitter ions (Er³⁺ or Tm³⁺) are located in the core while the Yb³⁺ sensitizer is doped in the shell layer. The core particles are synthesized using a hydrothermal growth process with growth control between 40-500 nm. Afterwards, a shell layer is deposited using a sol-gel method for shell thickness up to 30 nm. The particles were shown to have an upconversion luminescence emission in the blue, green, and red spectral region upon excitation with 980 nm light allowing for the barcoding of three different treatment protocols. The ratio of intensity of the different emission peaks were engineered through the dopant type, concentrations, and location within the core-shell structure. As a proof-of-concept, combinations of one, two, and three different types of nanoparticles were encapsulated in aqueous droplets in the array to demonstrate the ability to selective tag individual droplets. In order to determine the applicability of the nanoparticles as a means for droplet barcoding, viability studies were performed using different sized nanoparticles across a range of concentrations in several model cancer cells lines including HeLa, OPM2, THP-1, and HCT116 cells. This work provides the technological first step for a novel, antibody-free method to barcoding droplets to increase the throughput and utility of microfluidic droplet trapping arrays as a technique for personalized medicine.