Some preliminary results and experimental details of Near-field Scanning Optical Microscopy (NSOM) operation in liquids have been reported by us earlier(1-4). Here we present the first use of custom made polystyrene/poly (methyl methacrylate) (PMMA) optical fibers to assemble new NSOM probe/sensor for operation in liquids. Assembled NSOM probe has quite large quality factor Q ranging 2000-6000 in air(1), and 300-900 when immersed 0.2-0.3 mm deep into the water. Such montage demonstrates high mechanical durability permitting to scan different samples during many hours or even days, and overall low cost in comparison with NSOM probes based on glass optical fibers. A specially prepared optical fiber with 125 mu m diameter (from Paradigm Optics Company, USA) (polystyrene core diameter is 0.85 mu m, n(core) = 1.59 and PMMA cladding, n(core) = 1.49) was chemically etched using a 9: 1 mixture of dichloromethane and ethyl acetate(2). As result of the etching, a smooth and sharp tip is formed with a typical radius of the curvature equal to 50 - 170 nm. For completeness, earlier unpublished images of living Picocyanobacteria bacteria obtained using glass fiber-made NSOM probes are also presented.