We present a microfluidic 'megapixel' digital PCR device that uses surface tension-based sample partitioning and dehydration control to enable high-fidelity single DNA molecule amplification in 1,000,000 reactors of picoliter volume with densities up to 440,000 reactors cm(-2). This device achieves a dynamic range of 10(7), single-nucleotide-variant detection below one copy per 100,000 wild-type sequences and the discrimination of a 1% difference in chromosome copy number.

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Advancements in biomedical imaging require the development of optical contrast agents at an emission region of low biological tissue absorbance, fluorescence, and scattering. This region occurs in the red to near-IR (>600 nm) wavelength window. Quantum dots (Qdots) are excellent candidates for such applications. However, there are major challenges with developing high optical quality far-red- to near-IR-emitting Qdots (i.e., poor reproducibility, low quantum yield, and lack of photostability). Our aim is to systematically study how to prepare alloyed CdTe x Se1-x with these properties. We discovered that the precursor concentrations of Te-to-Se and growth time had major impacts on the Qdot's optical properties. We also learned that the capping of these alloyed Qdots were difficult with ZnS but feasible with CdS because of the ZnS's lattice mismatch with the CdTe x Se1 - x . These systematic and basic studies led to the optimization of synthetic parameters for preparing Qdots with high quantum yield (>30%), narrow fluorescence full width at half-maxima (<50%), and stability against photobleaching (>10 min under 100W Hg lamp excitation with a 1.4 numerical aperture 60× objective) for biomedical imaging and detection. We further demonstrate the conjugation of biorecognition molecules onto the surface of these alloyed Qdots and characterize their use as contrast agents in multicolored and ultrasensitive imaging.