One-pot synthesis to prepare lignin/photoacid nanohybrids for multifunctional biosensors and photo-triggered singlet oxygen generation

This study presents a green, simple, and efficient one-pot synthesis approach for a sustainable lignin nanoparticle biosensor (AL-Por-PP). Lignin was incorporated in a typical 5-5′ linkage interunit for developing azo-coupling under mild conditions. The precursors of this biosensor were targeted to lignin fractionation products, including alkali lignin (AL) and 2-phenylphenol (PP). They were linked by a modified porphyrin (Por), a sophisticated structure in the plant photosynthetic system. The lignin nanoparticles were investigated by various spectroscopic techniques (i.e., heteronuclear single quantum correlation HSQC-NMR, photoluminescence spectroscopy and time-resolved transient state spectroscopy) to characterize the structural and photochemical properties. This green biosensor showed superior harnessing abilities for excited state proton transfer (ESPT) photochemical dynamics of the grafted PP moieties. Lignin provided a stable microenvironment in broad pH ranges (pH 2 to 9) and various anion environments by forming a lignin nanosphere to encapsulate the excited PP moieties, offering a nano-buffering effect on these moieties via the intimate hydrogen bond networking interactions with the functional groups substituted on the lignin backbone. Moreover, AL-Por-PP demonstrated an outstanding selectivity of fluorescence responses to an essential index of asthma and lung cancer, bisulfite ions, in the concentration range of 1 to 20 μM (R2 = 0.99) which extends to live cell imaging. This study offers a sustainable and promising approach for extending the functionalities of lignin and highlights the prospects of valorizing lignin and plant extracts for biomass-based molecular device development and applications.