LAUSR

Food, chemicals, agricultural products, drugs, and vaccines should be transported and stored within an appropriate low-temperature range, following cold chain logistics. Violations of the required temperature regime are generally reported by time-temperature indicators; however, current sensors do not cover a sufficiently broad low-temperature range and may lack thermal and photostability. Here, we report a nanostructured solvatochromic temperature indicator formed from cellulose nanocrystals decorated with carbon dots (C-dots). The indicator utilizes a strong nonlinear dependence of photoluminescence of C-dots on the composition of water/dimethyl sulfoxide (DMSO) solvent and a composition-dependent variation of the melting temperature of the water/DMSO mixture. Exceeding the temperature of the frozen mixed solvent above a designated threshold value results in solvent melting, flow, and impregnation of the nanostructured film, thus causing an irreversible change in the intensity and wavelength of photoluminescence emission of the film, which is reported both qualitatively and quantitatively. The indicator covers a temperature range from -68 to +19 °C and is cost-efficient, portable and photo- and thermostable.