An optical signal transmittance based system/kit for point-of-care quantification of biomarker samples comprising: a sample stage including a detection unit; an optical transmission unit; and signal processing unit operatively connected to said optical transmission unit wherein said sample stage hosts a paper based reactive substrate being a light transmittable reactive substrate as said detection unit; said optical transmission unit comprises an illumination source and a photodetector such that light from the light source falls on the photodetector after being transmitted through said paper based reactive substrate; said paper based reactive substrate comprises a colored reagent which upon reaction with said biomarker leads to a variation in color intensities of said paper based reactive substrate so that transmitted quantifiable colorimetric optical signal therethrough is proportional to concentration of the said biomarker said photodetector is a light dependent resistor photodetector configured to transduce said quantifiable colorimetric optical signal transmitted through the paper based reactive substrate into analog electrical signals proportionate to the biomarker concentration; said signal processing unit is operatively connected to said photodetector to convert said analog electrical signals into digital display signals and includes a microprocessor to facilitate a single step signal processing without loss of the optical signal so as to provide a ready and fast direct point of care quantification of biomarker samples; wherein said sample stage further comprises a dark/black substrate chamber sized to receive said paper based reactive substrate with dark conditions around said paper based reactive substrate, said dark/black chamber having an opening bored therein configured to house the photodetector and another opening for allowing the light source through said dark/black chamber in a manner that: illumination from the light source falls directly on the paper based reactive substrate positioned inside the chamber through one of the said openings and is transmitted through said paper based reactive substrate through the other opening and into the photodetector; and a compact optical transmission unit with respect to said sample stage is provided. a sample stage including a detection unit; an optical transmission unit; and signal processing unit operatively connected to said optical transmission unit wherein said sample stage hosts a paper based reactive substrate being a light transmittable reactive substrate as said detection unit; said optical transmission unit comprises an illumination source and a photodetector such that light from the light source falls on the photodetector after being transmitted through said paper based reactive substrate; said paper based reactive substrate comprises a colored reagent which upon reaction with said biomarker leads to a variation in color intensities of said paper based reactive substrate so that transmitted quantifiable colorimetric optical signal therethrough is proportional to concentration of the said biomarker said photodetector is a light dependent resistor photodetector configured to transduce said quantifiable colorimetric optical signal transmitted through the paper based reactive substrate into analog electrical signals proportionate to the biomarker concentration; said signal processing unit is operatively connected to said photodetector to convert said analog electrical signals into digital display signals and includes a microprocessor to facilitate a single step signal processing without loss of the optical signal so as to provide a ready and fast direct point of care quantification of biomarker samples; wherein said sample stage further comprises a dark/black substrate chamber sized to receive said paper based reactive substrate with dark conditions around said paper based reactive substrate, said dark/black chamber having an opening bored therein configured to house the photodetector and another opening for allowing the light source through said dark/black chamber in a manner that: illumination from the light source falls directly on the paper based reactive substrate positioned inside the chamber through one of the said openings and is transmitted through said paper based reactive substrate through the other opening and into the photodetector; and a compact optical transmission unit with respect to said sample stage is provided.