A method of detecting a first target in a biological sample, comprising: contacting the biological sample with a first detection probe comprising an oligonucleotide fragment or an antibody of a particular species capable of specifically binding to the first target, wherein the oligonucleotide fragment includes a hapten; contacting the biological sample with a first labeling conjugate including an anti-species or anti-hapten antibody coupled to a first enzyme, wherein the first enzyme is an oxidoreductase or peroxidase, and wherein the first labeling conjugate, through its inclusion of an anti-species or anti-hapten antibody, binds selectively to the first detection probe; contacting the biological sample with a first signalling conjugate comprising a first latent reactive moiety and a first chromogenic moiety; illuminating the biological sample with a spectrally narrow light source having a spectral emission with a full-width half-max (FWHM) of between 30 nm and 250 nm; and detecting the first target through detecting a first colored signal selected from red, orange, yellow, green, indigo, or violet, the first colored signal associated with a spectral absorbance associated with the first chromogenic moiety of the first signalling conjugate; wherein the first enzyme catalyzes conversion of the first latent reactive moiety into a first reactive moiety, which covalently binds to the biological sample proximally to or directly on the first target by reacting with a tyrosine residue of the biological sample, the first labeling conjugate, the first detection probe, or combinations thereof; wherein the first latent reactive moiety has the general formula wherein R 25 is selected from the group consisting of hydroxyl, ether, amine, and substituted amine; R 26 is selected from the group consisting of alkyl, alkenyl, alkynyl, aryl, heteroaryl, -OR m, -NR m, and -SR m, where m is 1-20; n is 1-20; Z is selected from the group consisting of oxygen, sulfur, and NR a where R a is selected from the group consisting of hydrogen, aliphatic, aryl, and alkyl aryl; and wherein the spectral absorbance associated with the first chromogenic moiety of the first signalling conjugate has a full-width half-max (FWHM) of between 30 nm and 250 nm. contacting the biological sample with a first detection probe comprising an oligonucleotide fragment or an antibody of a particular species capable of specifically binding to the first target, wherein the oligonucleotide fragment includes a hapten; contacting the biological sample with a first labeling conjugate including an anti-species or anti-hapten antibody coupled to a first enzyme, wherein the first enzyme is an oxidoreductase or peroxidase, and wherein the first labeling conjugate, through its inclusion of an anti-species or anti-hapten antibody, binds selectively to the first detection probe; contacting the biological sample with a first signalling conjugate comprising a first latent reactive moiety and a first chromogenic moiety; illuminating the biological sample with a spectrally narrow light source having a spectral emission with a full-width half-max (FWHM) of between 30 nm and 250 nm; and detecting the first target through detecting a first colored signal selected from red, orange, yellow, green, indigo, or violet, the first colored signal associated with a spectral absorbance associated with the first chromogenic moiety of the first signalling conjugate; wherein the first enzyme catalyzes conversion of the first latent reactive moiety into a first reactive moiety, which covalently binds to the biological sample proximally to or directly on the first target by reacting with a tyrosine residue of the biological sample, the first labeling conjugate, the first detection probe, or combinations thereof; wherein the first latent reactive moiety has the general formula wherein R 25 is selected from the group consisting of hydroxyl, ether, amine, and substituted amine; R 26 is selected from the group consisting of alkyl, alkenyl, alkynyl, aryl, heteroaryl, -OR m, -NR m, and -SR m, where m is 1-20; n is 1-20; Z is selected from the group consisting of oxygen, sulfur, and NR a where R a is selected from the group consisting of hydrogen, aliphatic, aryl, and alkyl aryl; and wherein the spectral absorbance associated with the first chromogenic moiety of the first signalling conjugate has a full-width half-max (FWHM) of between 30 nm and 250 nm.