The present invention relates to a nanoparticle comprising self-assembled crosslinked, amphiphilic block copolymers and at least one immobilized dye, wherein the self-assembled, crosslinked, amphiphilic block copolymers comprise a hydrophilic block and a hydrophobic block, wherein the self-assembled, crosslinked, amphiphilic block copolymers are self-assembled to form a core of the nanoparticle comprising a hydrophobic block, wherein the hydrophobic block is derived from at least one pendant multifunctional crosslinked alkoxy silane or amino silane moiety, and an exterior of the nanoparticle comprising a hydrophilic block, and wherein the immobilized dye is immobilized in the core.