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Letter

Selective Probing and Imaging of Cells with Single Walled Carbon Nanotubes as Near-Infrared Fluorescent Molecules

Supporting Info

Kevin Welsher,^† Zhuang Liu,^† Dan Daranciang, and Hongjie Dai*

Department of Chemistry, Stanford University, Stanford, California 94305

Nano Lett., 2008, 8 (2), pp 586–590

DOI: 10.1021/nl072949q

Publication Date (Web): January 16, 2008

†

These authors contributed equally to this work.

Corresponding author. E-mail: hdai@stanford.edu.

Abstract

Fluorescent molecules emitting in the near-infrared (NIR, wavelength 0.8−2 μm) are relatively scarce and have been actively sought for biological applications because cells and tissues exhibit little auto-fluorescence in this region. Here, we report the use of semiconducting single-walled carbon nanotubes (SWNTs) as near-infrared fluorescent tags for selective probing of cell surface receptors and cell imaging. Biologically inert SWNTs with polyethyleneglycol functionalization are conjugated to antibodies such as Rituxan to selectively recognize CD20 cell surface receptor on B-cells with little nonspecific binding to negative T-cells and Herceptin to recognize HER2/neu positive breast cancer cells. We image selective SWNT−antibody binding to cells by detecting the intrinsic NIR photoluminescence of nanotubes. We observe ultralow NIR autofluorescence for various cells, an advantageous feature over high autofluorescence and large variations between cells lines in the visible. This establishes SWNTs as novel NIR fluorophors for sensitive and selective biological detections and imaging in vitro and potentially in vivo. Further, our results clearly show that the interactions between carbon nanotubes and living cells are strongly dependent on surface functionalization of nanotubes.