Transdermal alcohol biosensors have the ability to detect the alcohol that emanates from the bloodstream and diffuses through the skin. However, previous biosensors have suffered from long-term fouling of the sensor element and drift in the resulting sensor readings over time. Here, we report a wearable alcohol sensor platform that solves the problem of sensor fouling by enabling drift-free signals in vivo for up to 24 h and an interchangeable cartridge connection that enables consecutive days of measurement. We demonstrate how alcohol oxidase enzyme and Prussian Blue can be combined to prevent baseline drift above 25 nA, enabling sensitive detection of transdermal alcohol. Laboratory characterization of the enzymatic alcohol sensor demonstrates that the sensor is mass-transfer-limited by a diffusion-limiting membrane of lower permeability than human skin and a linear sensor range between 0 mM and 50 mM. Further, we show continuous transdermal alcohol data recorded with a human subject for two consecutive days. The non-invasive sensor presented here is an objective alternative to the self-reports used commonly to quantify alcohol consumption in research studies.

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follow Gay Lussac's law, i.e., its volume will increase by a definite increment for each rise of 1". Or, supposing that volume be maintained constant, its pressure will increase by a definite increment for each rise of 1" ; and from these statements, both of which are true, i t may he deduced that the product of pressure and volume, that is, the volume energy, will increase by definite increments for equal rises of temperature. This increment, supposing the gas to have been originally measured a t Oo, amounts to 1/273 of the original product of pressure aud volume for each degree centigrade. If, as is now customary, we choose as the unit of volume of a gas the volume in litres occupied by the molecular weight expressed in grams, and as unit of pressure an atmosphere, and if we reckon temperature from absolute zero, the numerical value of R, the factor by wbich absolute temperature must be multiplied in order tha.t it may be equated with the volume energy of the gas, is 0.0819 ; t)hus, pv = 0.0819T. If, then, in investigating an unknown gas or vapour, we happened to find that its volume energy increased proportiouately t o the absolute temperature, and that the factor necessaryfor the above equation was 0.0819, we should be justified in assuming that the molecular weight chosen in expressing v was the correct one. But if a different factor were found necessary, for instance, the factor 0.0819 x 2, o r 0.1638, we shonld conclude that the number chosen for the molecular weight, and consequently for the volume of the gas, was twice as great as it should have been. And i f it were found, moreover, that the actual factor were some number intermediate between 0.0819 and 0.1638, the deduction would follow that we were dealing with a mixture. If, lastly, the value of the factor mere found t o alter with rise of temperature, it would follow that the mixture was altering the relative amounts of its constituents as the temperature rose ; the relation between volume energy and temperature would then no longer be a rectilinear, but a curvilinear, one ; and the composition of the mixture could be deduced at any given temperature by comparison of the slope of the tangent to the curve at that temperature with the slope of the normal line, expressed by the number 0.0819. And the ratio of the normal factor, 0.0819, to the number found would give the number of simple molecules which had coalesced to form a complex molecule. This method would offer 110 advantage in determining the molecular weight of a gas, because the ordinary application of Avogadro's law is much more direct and simple, and involves precisely the same data. But by considering it, we may obtain a clearer conception of the method to be described, by which the molecular weights of sub