Cobalt Porphyrin–Chitosan Microspheres for Biosensing and Anticancer Therapy

Cobalt tetraphenylporphyrinate (CoTPP) has several properties that make it ideal for biomedical applications. It shows strong fluorescence, enabling sensitive optical biosensing; nonlinear optical activity (SHG/THG), which allows high-resolution, noninvasive imaging; photoresponsive dynamic behavior, where laser irradiation induces motion that could be exploited for dynamic anticancer therapies; and light-induced magnetic enhancement, potentially useful for hyperthermia or magnetic-field–based cancer treatments. However, CoTPP powder is not biocompatible and cannot be easily delivered to cells or tissues.

Domenica Marabello, Università degli Studi di Torino, Italy, and colleagues have created microspheres combining CoTPP with chitosan, a biocompatible material. The CoTPP–chitosan microspheres (CoTPP-CS-MPs) were prepared using an oil-in-water emulsion method. Their structure was characterized using optical, scanning, and transmission electron microscopy, as well as X-ray diffraction, and their optical behavior was tested with a high-resolution microscope for second-harmonic generation (SHG). SHG is a nonlinear optical process in which two photons of the same frequency interact with a non-centrosymmetric material to produce a new photon with twice the frequency and half the wavelength of the original light. This is useful for high-resolution, noninvasive bioimaging.

The team found that the microspheres combine sensing and therapeutic functions in a single, biocompatible material, offering a promising approach for targeted, low-side-effect cancer therapies and advanced biosensing.

The CoTPP-CS microspheres showed strong SHG, comparable to pure CoTPP powder, and retained porphyrin’s natural fluorescence, allowing them to act as optical biosensors. When exposed to laser light, the microspheres displayed physical movement and dynamic changes similar to those observed in CoTPP powder, suggesting potential applications in dynamic anticancer therapies, such as mechanically stimulating or targeting tumor cells. Based on prior studies of CoTPP, the microspheres may also show laser-induced magnetic enhancement, which could be exploited in hyperthermia or magnetic-field–based treatments.

By combining fluorescence, SHG, dynamic motion, and potential magnetic response, these microspheres are promising candidates for multitheranostic applications—simultaneous biosensing and therapy. The chitosan coating ensures low toxicity and good compatibility with biological tissues, which is crucial for practical biomedical applications.