Metal carbonyls for bio-imaging and -sensing
Date of Issue2017
School of Physical and Mathematical Sciences
Singapore Bioimaging Consortium, A*STAR, Singapore
Metal carbonyls, a class of organometallic complexes that consist of carbon monoxide (CO) ligands coordinated to a metal center, show intense CO vibrational frequencies in the mid-infrared (IR) 2200-1800 cm-1. This region is unique to the metal carbonyl species and is typically free of interference by other biomolecules. This property can be put to good use for mid-IR bio-sensing, which was first demonstrated by Jaouen and co-workers in the development of IR-based quantitative assays for detecting various biomolecules. In this thesis, the concept is extended to surface-enhanced Raman spectroscopy (SERS) through the development of metal carbonyl-based Raman reporters. The conjugation of two classes of metal carbonyls, namely, metal carbonyl clusters and mononuclear half-sandwich metal carbonyl complexes, onto colloidal gold nanospheres gave good CO vibrational stretches in the 1800-2200 cm-1 region. Alterations to the ligand sphere and the charge (for cluster complexes) were found to be effective in tuning the CO vibrational stretches over a wide frequency range. It was also observed that the SERS enhancement was highly dependent on the extent of aggregation of the colloid. In another extension, a SERS-active planar substrate was utilized in tandem with a triosmium carbonyl cluster-boronic acid conjugate acting as a secondary saccharide probe, in a sensitive and selective SERS-based glucose assay. While investigating extension of this idea to the detection of cancer cells via their surface glycans, thiolato triosmium carbonyl clusters of the type Os3(u-H)(u-SAryl)(CO)10 were found to be cytotoxic. Cell death was found to be via the induction of apoptosis. Metal carbonyl clusters were also demonstrated to be good contrast agents for photoacoustic (PA) imaging. The cluster nuclearity was shown to be a useful parameter for fine-tuning the absorption wavelength, as increasing the cluster nuclearity shifted the absorption into the near-IR region. The high nuclearity carbonyl cluster [Os10(u6-C)(CO)24]2- was shown to exhibit good PA properties in the NIR region, and its sodium salt was applied successfully for the whole body PA imaging of live mice.