Table 2.

Challenges and strategies to improve the performance of colorimetric systems for the detection of bacterial contamination.

Challenge	Performance Improvement Strategy	Reference(s)
Sensitivity	Use of pH-responsive NPs Use of a dual-readout method with chromogens for fluorescence and visible color Use of dual-readout with redox-active molecules with electrochemical and optical properties Selection of optimal pH-responsive molecules and chromogens Combination of signal amplification methods Use of a signal enhancer	[22] [36] [34] [19] [56,57,69,81,82,83,84] [70,71,72]
Simple operation	Use of a regent-embedded multi-layered paper structure Use of Ag ion without fabrication and functionalization of NPs Combined with an automation device	[32] [21] [22]
Correct signal in complex real samples	Based on the catalytic activity of mimetic enzymes (functional NPs or nanostructure)	[37,38,39,40,41,42,43,44]
Multiplexing capability	Combined with an automation device Based on multiple chromogenic or cellular metabolic reactions	[22] [31]
Quantification and expansion of analyzed spectra	Use of RGB analysis software on a smartphone	[22,23,34,36]