Green Strategies for Sol-Gel Immobilization of Biomolecules and Carbon Nanotubes

Immobilization of enzymes, cells, carbon nanotubes and organelles has been relevant for numerous applications including energy harvesting and sensing. One of the important class of molecules are enzymes that are key to new processes because they are environmentally friendly, expensive, fragile, reduce hazardous waste, and one the best catalyst known to mankind, thus the soft immobilization strategies are highly desired. One of the key immobilization techniques used is Sol-gel technique. Sol is generally referred to as a collection of colloidal silica particles ranging from 1-1000 nm in a liquid phase, and sol-gel is obtained by enhancing the interactions between these colloidal particles resulting in the formation of a gel like material.
Several methods have been explored during last few decades to efficiently immobilize biomolecules in sol-gel mainly because of the advantage of room-temperature synthesis and enhanced stability of immobilized enzymes. The common silica precursors include tetra alkoxy silanes, sodium silicate, silaffin polypeptides and even hydrophobic silica precursors. Of all these methods, the most common sol-gel synthesis revolve around a two-step process in which, an alkoxy silane precursor is hydrolyzed using an acid/base catalyst in a water/alcohol environment followed by removal of toxic solvent and further followed by addition of biomolecules to the system.
I will show a CVD approach that has been developed by our group to bulk immobilization of a wide variety of molecules including enzymes, organelles, cells, sensitive lipid bilayer based systems and carbon nanotubes. Typically, the process is a simple one-step process that involves the exposure of an aqueous solution to the vapors of tetramethoxy silane at room temperature for a desired amount of time. This process follows key principals of green chemistry including:
Prevention (No Waste materials), Economy (All chemicals are utilized completely), Less hazardous chemical Synthesis (No acid and base catalyst), Safer solvents (Aqueous route), Energy Efficiency (Ambient Temperature and pressure), and Safe Chemistry (and minimal accident issues and hazards)