A method for determining a ratio of hemoglobin absorption within a biological tissue using a handheld device is provided. The method includes focusing at least one light pulse into a predetermined area inside an object using at least one excitation wavelength, wherein a fluorescence signal is based on at least a local excitation optical fluence and properties of fluorophores in the predetermined area. The method further includes receiving a photoacoustic signal emitted by the object in response to the at least one light pulse, the photoacoustic signal being a product of the local excitation optical fluence, an optical absorption coefficient of hemoglobin, and an acoustic detection sensitivity. The method further includes determining the ratio of hemoglobin absorption based on a hemoglobin absorption coefficient that is based at least partially on the fluorescence signal and the photoacoustic signal.