Micro-Raman Spectroscopy of Silver Nanoparticle Induced Stress on Optically-Trapped Stem Cells

We report here results of a single-cell Raman spectroscopy study of stress effects induced by silver nanoparticles in human mesenchymal stem cells (hMSCs). A high-sensitivity, high-resolution Raman Tweezers set-up has been used to monitor nanoparticle-induced biochemical changes in optically-trapped single cells. Our micro-Raman spectroscopic study reveals that hMSCs treated with silver nanoparticles undergo oxidative stress at doping levels in excess of 2 µg/ml, with results of a statistical analysis of Raman spectra suggesting that the induced stress becomes more dominant at nanoparticle concentration levels above 3 µg/ml

The experimental apparatus used in the present studies.

<p>(a) Schematic representation of the Raman Tweezers set-up. (b) Picture of the Raman Tweezers set-up showing the geometry of the trapping laser beam and the Raman probe laser beam.</p

Morphology of hMSC's (A) Control, and Ag NP treated with concentration (B) 1 µg/ml, (C) 2 µg/ml, (D) 3 µg/ml, (E) 4 µg/ml and (F) 5 µg/ml.

<p>Magnification 4×.</p

Raman frequency assignments of single control hMSC.

a<p>p:protein,</p>b<p>Phe: phenylalanine,</p>c<p>Tyr: tyrosine,</p>d<p>Met: methionine,</p>e<p>Trp: tryptophan,</p>f<p>NA: Nucleic Acids.</p><p>A,U,G,T,C denote ring breathing modes of nucleic acid bases adenine, uracil, guanine, thymine, and cytosine.</p

Phase contrast microscope image of control human Mesenchymal stem cells (hMSC) culture after passage 5.

<p>Magnification 4×.</p

PCA results in the form of a scatter plot depicting the Score of Factor 1 against the Score of Factor 2.

<p>Control, 1 µg/mL and 2 µg/mL NP treated cell spectra are clustered together (except one datum).</p

Flow cytometer CD Marker Expression for control hMSC (without Ag NPs).

<p>Flow cytometer CD Marker Expression for control hMSC (without Ag NPs).</p

Shows a typical baseline-corrected microRaman spectrum of an optically trapped hMSC (an image of which is shown).

<p>The laser power used for trapping (1064 nm wavelength) was 5 mW while the Raman spectrum was measured using a laser power of ∼20 mW (785 nm wavelength); the acquisition time was 120 s and 5 accumulations were made.</p