Spontaneously sp²-Carbonized Fluorescent Polyamides as a Probe Material for Bioimaging

Area of Science:

• Polymer Chemistry
• Materials Science
• Nanotechnology

Background:

• Polyamides (PA) are versatile polymers with diverse applications.
• Carbonized nanomaterials offer unique optical properties.
• Understanding fluorescence origins in such materials is crucial for advanced applications.

Purpose of the Study:

• To synthesize and characterize novel, spontaneously carbonized polyamides (PA1, PA2).
• To investigate the fluorescence properties and their dependence on excitation wavelength and pH.
• To explore the potential of these polyamides in bioimaging, particularly lysosome staining.

Main Methods:

• Polycondensation of dicarbonyl chloride and diamine under mild conditions.
• Knoevenagel-type side reactions leading to sp2-carbonization.
• Spectroscopic analyses (e.g., fluorescence spectroscopy) to determine structure and origin of emission.
• In vitro assays to evaluate cytotoxicity, biocompatibility, and cellular uptake (endocytosis).

Main Results:

• Successfully synthesized water-soluble and emissive polyamides (PA1, PA2).
• Fluorescence intensity and emission wavelength showed significant dependence on excitation wavelength and pH.
• The observed fluorescence is attributed to a π*-π transition in the enol form of the conjugated structure.
• PA2 demonstrated rapid endocytosis, low cytotoxicity, excellent biocompatibility, and specific lysosome staining.

Conclusions:

• The study elucidates the origin of fluorescence in spontaneously carbonized polyamides, linked to their conjugated enol structure.
• These novel polyamides exhibit promising characteristics for bioimaging, especially lysosome targeting.
• The findings contribute to understanding fluorescence in carbonized nanomaterials and pave the way for advanced bioimaging tools.