Patent ID: 8173973

Claim:
A method for measuring a fluorescent sample on a substrate, the method comprising: (a) exciting the fluocrescent sample with an exciting light source for the generation of a sample fluorescent optical signal and a substrate fluorescent optical signal; (b) substantially eliminating the substrate fluorescent optical signal and leaving the sample fluorescent optical signal; and (c) processing the sample fluorescence optical signal, wherein the substantially eliminating the substrate fluorescence signal comprises: (i) modulating the frequency of a light source to excite fluorophore of the sample according to a predetermined modulation frequency such that a phase difference between the sample fluorescence optical signal and the substrate fluorescence optical signal is substantially 90 degrees; (ii) generating a sine wave signal based on a unity-gain sine wave signal corresponding to the predetermined modulation frequency delayed by the phase of the substrate fluorescence optical signal; (iii) mixing the sine wave signal with an acquired signal corresponding to the fluorescence emission of the sample and the substrate, into at least one mixed signal; and (iv) filtering the at least one mixed signal to obtain a DC component of the fluorescence signal of the sample; and (v) wherein the fluorescence emission of the substrate is filtered and the DC component is proportional to the concentration of the fluorescence signal of the sample.