A method for performing a Western Blot assay, the method comprising: providing a sample supported on a membrane, the sample comprising a plurality of proteins, the plurality of proteins comprising a plurality of target proteins (408, 808); performing a probing process by contacting the sample with a fluorescent resonance energy transfer (FRET) solution and allowing the probing process to proceed for a probing time period, wherein: the probing process produces a plurality of labeled target proteins to which first probes and second probes are bound; the first probes each comprise a donor chromophore (742, 842), the second probes each comprise an acceptor chromophore (746, 846), and the donor chromophore (742, 842) and the acceptor chromophore (746, 846) are effective as a donor-acceptor pair for FRET; and the FRET solution comprises the first probes, or the second probes, or both the first probes and the second probes; and while performing the probing process, measuring the labeled target proteins by: irradiating the membrane with an excitation light (532, 732) to excite the donor chromophores (742, 842), wherein in each labeled target protein, the excited donor chromophore (742, 842) transfers energy to the acceptor chromophore (746, 846) by FRET and, in response, the labeled target protein emits an emission light; and measuring an intensity of the emission light. providing a sample supported on a membrane, the sample comprising a plurality of proteins, the plurality of proteins comprising a plurality of target proteins (408, 808); performing a probing process by contacting the sample with a fluorescent resonance energy transfer (FRET) solution and allowing the probing process to proceed for a probing time period, wherein: the probing process produces a plurality of labeled target proteins to which first probes and second probes are bound; the first probes each comprise a donor chromophore (742, 842), the second probes each comprise an acceptor chromophore (746, 846), and the donor chromophore (742, 842) and the acceptor chromophore (746, 846) are effective as a donor-acceptor pair for FRET; and the FRET solution comprises the first probes, or the second probes, or both the first probes and the second probes; and the probing process produces a plurality of labeled target proteins to which first probes and second probes are bound; the first probes each comprise a donor chromophore (742, 842), the second probes each comprise an acceptor chromophore (746, 846), and the donor chromophore (742, 842) and the acceptor chromophore (746, 846) are effective as a donor-acceptor pair for FRET; and the FRET solution comprises the first probes, or the second probes, or both the first probes and the second probes; and while performing the probing process, measuring the labeled target proteins by: irradiating the membrane with an excitation light (532, 732) to excite the donor chromophores (742, 842), wherein in each labeled target protein, the excited donor chromophore (742, 842) transfers energy to the acceptor chromophore (746, 846) by FRET and, in response, the labeled target protein emits an emission light; and measuring an intensity of the emission light. irradiating the membrane with an excitation light (532, 732) to excite the donor chromophores (742, 842), wherein in each labeled target protein, the excited donor chromophore (742, 842) transfers energy to the acceptor chromophore (746, 846) by FRET and, in response, the labeled target protein emits an emission light; and measuring an intensity of the emission light.