Autofluorescence is the natural fluorescent emission from biological structures or other substances in the presence of excitation light. This can be the source of background noise (background fluorescence) which can cause complications in imaging biological samples such as cells or tissues. Other reasons such as non-specific absorption can also give rise to the background noise. Microfluidic chips have been extensively used in biology research, for example, organ-on-a-chip, drug toxicity screening, or nucleic acid amplification microfluidic devices. These microchips can be fabricated using a wide variety of materials including elastomers and thermoplastics. The autofluorescent properties of the material should be considered before the design and fabrication of the microfluidic devices that involve fluorescent imaging to reduce the measurement errors and complications.
Various materials have been used for the fabrication of microfluidic chips such as PDMA, PMMA, and Polycarbonate (PC). It is of crucial importance to take the autofluorescent properties of the material of choice into account while doing experiments to ensure minimum error in measurement and analysis.
It has been shown that for many plastics the autofluorescence decreases as the excitation wavelength increases. Therefore, the highest autofluorescence can be expected at ~ 400 nm excitation wavelength. However, with an increase in the wavelength, the autofluorescence dramatically decreases with the PDMS having the lowest autofluorescence at 633 nm among PMMA, PC, and COC. The autofluorescence of the most common material used in microfluidic chips, PDMS, is nearly constant compared to the aforementioned materials and is comparable to borofloat glass.