Water-Soluble Germanium(0) Nanocrystals: Cell Recognition and Near-Infrared Photothermal Conversion Properties

• Published in: Small (Weinheim an der Bergstrasse, Germany) Germany), 2007-04, Vol.3 (4), p.691-699
• Main Authors: Lambert, Timothy N., Andrews, Nicholas L., Gerung, Henry, Boyle, Timothy J., Oliver, Janet M., Wilson, Bridget S., Han, Sang M.
• Format: Article
• Language: English
• Subjects: Animals; Cattle; cell recognition; Dinitrobenzenes - chemistry; energy conversion; Fluoresceins - chemistry; germanium; Germanium - chemistry; Immunoglobulin E - chemistry; Light; Metal Nanoparticles - chemistry; Microscopy, Electron, Transmission; nanocrystals; Nanoparticles - chemistry; Nanotechnology - methods; semiconductors; Serum Albumin, Bovine - chemistry; Spectrometry, X-Ray Emission; Spectroscopy, Near-Infrared; Titanium - chemistry
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.200600529

Surfactant‐passivated germanium nanocrystals (Ge(0) NCs) 3–5 nm in diameter were synthesized and encapsulated with functionalized phospholipids to yield water‐soluble Ge(0) NCs. Upon encapsulation, the NCs retained their cubic crystalline phase and displayed good resistance to oxidation, as determined by transmission electron microscopy and X‐ray photoelectron spectroscopy. As a test of their cell compatibility, the ability of carboxyfluorescein (CF)‐labeled dinitrophenyl (DNP)‐functionalized Ge(0) NCs to crosslink dinitrophenol‐specific immunoglobulin E antibodies on the surface of mast cells (RBL‐2H3) was examined in vitro. Treatment with a multivalent DNP antigen (i.e., DNP‐Ge(0) NCs or CF‐DNP‐Ge(0) NCs) caused crosslinking of FcεRI receptors and cellular responses, which were evaluated with morphological and colorimetric assays and live‐cell fluorescence microscopy. Incubation of RBL‐2H3 cells with Ge(0) NCs for ≈24 h gave less than a 2 % increase in cell death as compared to DNP‐functionalized bovine serum albumin. When irradiated with near‐infrared (NIR) radiation (λexc=770 nm, 1.1 W cm−2) from a continuous‐wave Ti:sapphire laser, the bulk‐solution temperature of a toluene solution containing 20 mg mL−1 Ge(0) NCs increased by ≈35 °C within 5 min. Phospholipid‐encapsulated water‐soluble Ge(0) NCs at concentrations of 1.0 mg mL−1 also displayed stable photothermal behavior under repetitive and prolonged NIR laser exposures in water, to yield a temperature increase of ≈20 °C within 5 min (λexc=770 nm, 0.9 W cm−2). The photothermal efficiency of water‐soluble Ge(0) NCs compares favorably with a recent report for Au nanoshells. A signal achievement: Stable, water‐soluble, crystalline Ge(0) nanocrystals (NCs) were prepared and shown to be capable of inducing cell signaling in RBL‐2H3 mast cells with minimal toxicity. Both organic‐ and water‐soluble Ge(0) NCs exhibited photothermal behavior when excited with near‐infrared (NIR) radiation, even under repetitive and prolonged NIR laser exposure. The figure shows dye‐labeled receptors on RBL‐2H3 mast cells, crosslinked by derivatized Ge(0) NCs.