A method for calorimetry includes flowing a first fluid through a co-flow reactor microchannel having plural inlets and an outlet, the first fluid flowing through each of the inlets, and measuring transmission of light through a Nano Hole Array (NHA) sensor to obtain a baseline extraordinary optical transmission (EOT) measurement. The flow of the first fluid is stopped, the microchannel is emptied of the first fluid, and the first fluid and a second fluid are passed through the microchannel such that a reaction occurs, the first fluid flowing through a first of the inlets and the second fluid flowing through a second of the inlets. While flowing the first and second fluids, transmission of light through the NHA sensor is measured to obtain a reaction EOT measurement. A calorimetry measurement, indicative of energy released during the reaction, is calculated as a function of the baseline and reaction EOT measurements.