Reversible data encryption–decryption using a pH stimuli-responsive hydrogel

In this work, based on a pH-responsive hydrogel, we report on a reversible data encryption–decryption technique in which the pH channel is employed for data manipulation. Upon alkali or acid stimulation, the hydrogel exhibits a network expansion or shrinkage in response to the pH variations. In particular, pre-doping the hydrogel with silver ions, we demonstrate that data input can be encoded in the hydrogel platform through the direct writing and patterning of silver nanodots. By this means, the scattering signals from the patterned nanodot pixels are converted to the binarized data. Meanwhile, we show the threshold behaviour of the hydrogel system in which dynamic switching of the encoded plasmonic pattern to the optically resolvable/irresolvable state is viable only at finite pH values. By delicately matching pixel spacings of the encoded pattern and the diffraction limit of the deciphering microscopic system, reversible sub-diffraction limit data encryption is achieved by selectively imposing acid and alkali stimulations. The suggested strategy offers a potential solution for optical storage, multiplexed data manipulation, and optical data security.