Table 2.

Technologies for CL detectors implemented into paper-based portable immunosensors.

Detector for CL Paper-Based Immunosensor	Detection Principle	Pros	Cons
Photomultiplier tube (PMT)	Each PMT can detect just one wavelength. It captures emitted photons and its photocathode layer, then converts these photons to electricity. Dynodes are then used to multiply this charge multi-fold, making it readable for the instrument.	Excellent signal amplification Short response times High sensitivity Low noise	Expensive Large size Each wavelength needs a specific element High energy consumption Low design flexibility
Charged coupled device (CCD)	In a CCD image sensor, pixels represent the basic building blocks, and they are composed of p-doped metal–oxide-semiconductor (MOS) capacitors. Pixels allow the conversion of incoming photons into electron charges at the semiconductor-oxide interface; the CCD is then used to read out these charges.	Good sensitivity Small dark current Wide range of wavelength Compact High image quality	High power consumption Difficult system integration More expensive than CMOS
Complementary metal-oxide semiconductor (CMOS) sensor	CMOS has emerged as alternative to CCD. Differently from CCD, each pixel sensor unit has a photodetector.	Low-cost Wide range of wavelength Easy implementation into portable device (e.g., smartphone’s camera) Low power consumption High speed	Lower sensitivity respect CCD Large dark current
Thin-film photosensors	There is a wide variety of photosensors based on different materials but they are typically based on a p–n junction that converts light photons into current. The absorbed photons make electron–hole pairs in the depletion region.	Low-cost Easy implementation into portable device Low power consumption Possibility to develop disposable platforms based on thin-film photosensors Custom geometries can be developed	Large dark current Low thermal stability Low sensitivity