Provided herein are sensors, kits that include such sensors, and methods for making and using such sensors. The sensors permit detection of a broad array of target molecules, such as nucleic acids (e.g., DNA and RNA), proteins, toxins, pathogens, cells, and metals, and can be used in combination with pH meters and pH paper. Thus, this disclosure provides a new methodology that allows pH meters and pH paper to be used for the detection of analytes other than pH.
ACKNOWLEDGMENT OF GOVERNMENT SUPPORT
 This invention was made with government support under DE-FG02-08ER64568 awarded by the US Department of Energy and under ES16865 awarded by the National Institutes of Health. The government has certain rights in the invention.