Compositions, kits and methods useful for determining the concentration of proteins or peptides in samples by fluorometric and/or colorimetric detection. Rapid quantitation of proteins and peptides or peptide mixtures by the present compositions, kits and methods provide one or more advantages such as but not limited to, methods that work at room temperature, no requirement for elevated temperatures or long incubation times, high sensitivity, low S/N background, detection in large and small sample volumes, detection in samples containing detergents and organic solvents.

Chemoproteomic methods for detecting and profiling electrophilic post-translational modifications (PTMs) and oxidative PTMs in proteins are described. The methods including contacting a proteomic mixture with a probe having hydrazine and alkyne moieties or oxyamine and alkyne moieties to form a covalent linkage between the hydrazine or oxyamine moiety of the probe and the electrophilic PTM or oxidative PTM of the protein. The resulting alkyne-derivatized proteins are labelled with an azide modified tag via a click chemistry reaction. The labelled proteins can then be detected or profiled using techniques such as, for example, fluorescence imaging or mass spectrometry. Also described are protein conjugates having a covalent linkage formed by reaction of a hydrazine or oxyamine moiety of a probe with an electrophilic or oxidative PTM of a protein.

Peptide and/or protein quantitation methods, kits, and compositions, particularly useful for mass spectrometry, are provided herein based on a bathocuproine-based composition complex such as bathocuproinedisulfonic acid disodium salt hydrate complex. The methods are one-step rapid absorbance methods using small sample volumes. They produce a robust signal with high signal to background ratio and accurately quantitate even complex peptide mixtures with low variability and high sensitivity.

A method for detecting presence of protein or biofilm on a surface includes applying a composition to the surface, and observing a color reaction if protein or biofilm is present on the surface. The composition comprises a first part that includes copper sulfate and a second part that includes a reagent capable of reacting with the copper sulfate to produce a visible color reaction when contacted with protein or biofilm.