Indocyanine green-loaded microspheres as a near-infrared fluorescence marker for long-term localization of tumor sites

Purpose Noninvasive and real-time detection of tumor sites is highly important for precision cancer surgery. In this study, we developed indocyanine green (ICG)-loaded microspheres as near-infrared (NIR) fluorescence markers for the noninvasive and long-term localization of tumor sites. Methods Microspheres were prepared using a water-in-oil-in-water method to encapsulate ICGs into small and multiple separated pores inside the microspheres. Microspheres containing different amounts of Poloxamer 188 were evaluated both in vitro and in vivo. Results Encapsulation of ICG and the human serum albumin (HSA) complex in the microspheres showed 25-fold higher fluorescence signals than ICG alone. The addition of 1% poloxamer 188 (P-188) to the oil phase resulted in the highest fluorescence signal from the microspheres. When ICG-HSA-loaded microspheres with 1% P-188 were subcutaneously injected into SKH-1 hairless mice, strong fluorescence signals from the injection sites were detected for up to 30 d without a significant reduction in the NIR fluorescence intensity. Conclusion Biocompatible ICG dye-loaded microspheres have great potential as long-term fluorescent markers for imaging-guided precision surgery.