Noninvasive metabolic profiling using microfluidics for analysis of single preimplantation embryos.

Noninvasive analysis of metabolism at the single cell level will have many applications in evaluating cellular physiology. One clinically relevant application would be to determine the metabolic activities of embryos produced through assisted reproduction. There is increasing evidence that embryos with greater developmental capacity have distinct metabolic profiles. One of the standard techniques for evaluating embryonic metabolism has been to evaluate consumption and production of several key energetic substrates (glucose, pyruvate, and lactate) using microfluorometric enzymatic assays. These assays are performed manually using constriction pipets, which greatly limits the utility of this system. Through multilayer soft-lithography, we have designed a microfluidic device that can perform these assays in an automated fashion. Following manual loading of samples and enzyme cocktail reagents, this system performs sample and enzyme cocktail aliquotting, mixing of reagents, data acquisition, and data analysis without operator intervention. Optimization of design and operating regimens has resulted in the ability to perform serial measurements of glucose, pyruvate, and lactate in triplicate with submicroliter sample volumes within 5 min. The current architecture allows for automated analysis of 10 samples and intermittent calibration over a 3 h period. Standard curves generated for each metabolite have correlation coefficients that routinely exceed 0.99. With the use of a standard epifluorescent microscope and CCD camera, linearity is obtained with metabolite concentrations in the low micromolar range (low femtomoles of total analyte). This system is inherently flexible, being easily adapted for any NAD(P)H-based assay and scaled up in terms of sample ports. Open source JAVA-based software allows for simple alterations in routine algorithms. Furthermore, this device can be used as a standalone device in which media samples are loaded or be integrated into microfluidic culture systems for in line, real time metabolic evaluation. With the improved throughput and flexibility of this system, many barriers to evaluating metabolism of embryos and single cells are eliminated. As a proof of principle, metabolic activities of single murine embryos were evaluated using this device.