TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Xerogel: This comprises a group 3-5 oxide, optionally organically modified, e.g. silica, R-SiOn, R2SiOn, alumina and/or titania, where R is hydrogen, (epoxy)alkyl, aryl or aminoalkyl and n is 1 or 1.5, and it may include a mixture of such molecules. The content of (I) is 5-50wt.% on (A), which may be formed as powders, granules or coatings on a rigid or flexible carrier.Preferred Materials: (I) is e.g. a soluble nitrogen compound, e.g. an ammonium compound) or a salt of a trace element.Preparation: An inorganic nanosol, optionally organically modified, is first prepared by acid or alkaline hydrolysis of the corresponding silicon and/or metal alkoxide, in aqueous, organic or mixed solution. Particularly hydrolysis is with acid in aqueous alcohol, since the products then form strongly adherent, transparent films. Then an aqueous phosphate-containing solution of a nutrient is added, the mixture gelled (by neutralization or heating, or by coating on to a carrier and evaporation of solvent), and the composite gel dried. Drying is particularly in air and the gel is solidifed by heating to at most 100 degrees C.    TECHNOLOGY FOCUS - BIOLOGY - Preferred Nutrients: These are soluble carbohydrates, organic nitrogen sources (proteins, peptides, soya meal or yeast extract) or growth factors (vitamins, biotin, unsaturated fatty acids and special glycoproteins). EXAMPLE - A sol of silica content 4.2 wt.% and alcohol content about 70 % was prepared by acid hydrolysis of tetraethoxysilane. It (10 ml) was mixed with phosphate buffer (pH 4.8) containing 10 % pancreatic peptone (3 ml) and the mixture coated on to both slides of a glass plate, which was then dried for 1 hour at 60 degrees Centigrade. The plate was disinfected with ethanol and contacted for 3 minutes with 1 ml of a suspension of 1.6 x 10 to the power of 6 colony-forming units (cfu) of Bacillus sphaericus JG-A12, then incubated at 40 degrees Centigrade in a Greiner tube. After 3 weeks, the surface was rinsed with 5 ml physiological saline and the number of cfu units counted. The result was 1.8 x 10 to the power of 5 compared to 1.8 x 10 to the power of 3 for an untreated glass slide.