Described here are patches and methods for measuring glucose in sweat (and tears and the like). In general, the patches comprise an adhesive layer adapted to bond to skin of an individual, a substrate layer disposed over the adhesive layer and comprising a glucose sensing complex including a chromogen that changes color in the presence of certain concentrations of glucose, and a cover. In typical embodiments, the substrate layer has elements formed to direct and accumulate sweat that migrates from the skin of the individual to the glucose sensing complex. Methods of using the invention can comprise cleaning the skin surface, collecting sweat in a patch comprising this microfluidic constellation of elements, and observing concentrations of glucose collected in the sweat, for example either visually, or by using a smartphone or other computer processing device.