Fluorescent dermal tattoo biosensors for electrolyte analysis

Dehydration, the abnormal depletion of body fluid, has been considered to greatly affect metabolic activities that may cause electrolyte disorder. However, current diagnostic approaches often fail to provide rapid and accurate electrolyte measurements in point-of-care settings. Here, fluorescent dermal tattoo sensors were developed to monitor electrolytes (e.g. H⁺, Na⁺, and K⁺ ions) in dermal interstitial fluids by using a customizable tattoo sensing platform. This platform consists of multiplexed fluorescent sensors including seminaphtorhodafluor, fluorescent diaza-15-crown-5 ether, and fluorescent diaza-18-crown-6 ether tattooed in the skin tissue. A portable optical readout device comprised of a smartphone, excitation light sources, and optical bandpass filters is developed to measure the fluorescence emission intensity of the tattoo sensors. The smartphone readout application features a user interface and a compensation algorithm to estimate electrolyte concentrations. Ex vivo studies in porcine skin tissues show that the tattooed sensors could provide quantitative results of electrolytes in dermis. These dermal sensors detect pH value, Na⁺ and K⁺ ions in the ranges of 6.6–7.6, 100−175 mmol L⁻¹, and 2.0–6.0 mmol L⁻¹. The detected emission intensities are converted to the concentration values of electrolytes and display in the smartphone diagnostic report. The dermal tattoo sensor may enable continual assessment of hydration status in point-of-care settings.