Delivery of nanogram payloads using magnetic porous silicon microcarriers.

A transport and delivery system for nanogram quantities of molecular species that does not use microfluidic channels, pumps, or valves is described. Microparticles consisting of magnetic porous silicon are prepared, and loading and delivery of an enzymatic payload are demonstrated. The high porosity (60%) porous Si host particles are made magnetic by infusion of superparamagnetic iron oxide nanoparticles (30 nm-diameter magnetite, Fe(3)O(4)) under oxidative conditions. After magnetite incorporation, the porous microparticle is still empty enough to accommodate nanogram quantities of a molecular payload; the enzymes horseradish peroxidase or pronase E are used in the present work. The assembly can be transported to a microliter water droplet containing the enzyme substrate with the aid of an external magnetic field. The enzyme is released into the droplet upon contact. The particles can be transported through air or a hydrocarbon liquid without loss in enzymatic activity of the payload.