Disclosed is a fluorescent conjugate comprising a biological reagent, a fluorescent molecule, and a means for impeding phototoxic degradation of the biological reagent. The impeding means can be a cross-linking substance having a long molecular distance, whereby the cross-linking substance links the fluorescent molecule and the biological reagent; a quencher of singlet oxygen; a quencher of a free radical; or a combination thereof. Also disclosed is a solution comprising a fluorescent conjugate of a biological reagent and a fluorescent molecule together with an oxygen depleting system.