Titanium nitride nanoparticles for laser nanowarming in cryopreservation

Cryopreservation by vitrification prevents ice formation during cooling but requires rapid and uniform rewarming to avoid devitrification and sample damage. Laser nanowarming using plasmonic nanoparticles has emerged as a promising solution. Yet, gold nanorods (GNRs), a widely used plasmonic nanomaterial for laser nanowarming, are limited by high cost, surfactant dependence, and reduced stability in cryoprotectant (CPA) solutions. Here, we evaluate titanium nitride nanoparticles (TiN NPs) as an alternative for nanowarming 1 µL vitrified CPA droplets containing Artemia salina cysts and investigate the role of surface modification to enable direct comparison with ligand-stabilized GNRs. Bare TiN, TiN methoxy polyethylene glycol silane (mPEG-Silane), and TiN (3-aminopropyl)triethoxysilane (APTES) NPs enabled efficient rewarming across a broad range of conditions, with bare TiN achieving near-control hatchability (∼85%) at 400 µg mL^-1 under 2 ms pulse durations (∼3 J). Surface modification improved dispersion and tuned heating behavior, with TiN-mPEG-Silane reducing the optimal concentration to 300 µg mL^-1 and TiN-APTES providing more consistent performance across conditions, demonstrating that modifying TiN enhances colloidal stability and promotes a more favorable absorption-to-scattering balance for uniform heating. Additionally, all TiN formulations remained stable in CPA for 14 days and exhibited minimal toxicity to live Artemia for up to 48 hours. In contrast, under the CPA formulation investigated, the GNR formulation required substantially higher mass concentrations to achieve successful laser nanowarming and cyst hatching. Overall, TiN nanomaterials provide a cost-effective, thermally robust, and tunable platform for laser nanowarming. Under the experimental conditions investigated, TiN formulations achieved comparable or improved nanowarming outcomes while requiring substantially lower concentrations than the GNR formulation evaluated, offering a practical pathway to advance vitrification-based cryopreservation.