Imaging intracellular zinc by stimulated Raman scattering microscopy with a small molecule vibrational probe

Area of Science:

• Chemical biology
• Bioimaging
• Spectroscopy

Background:

• Stimulated Raman scattering (SRS) microscopy is a powerful bioimaging technique.
• Development of chemical probes for metal ion detection in biological systems, especially using SRS, lags behind instrumentation advances.
• Few responsive probes exist for dynamic detection of transient, low-abundance species like Zn2+.

Purpose of the Study:

• To design and apply CSZin, a novel small-molecule vibrational probe for the detection of Zn2+ in biological contexts.
• To demonstrate the utility of CSZin for SRS imaging of Zn2+ in vitro and in live cells.
• To explore the potential of CSZin for detecting other biologically relevant metal ions.

Main Methods:

• Design of CSZin, a spiropyran-based probe with a nitrile group sensitive to metal binding.
• Utilizing SRS microscopy for label-free vibrational imaging.
• In vitro and live-cell imaging experiments to detect Zn2+ ions.
• Analysis of SRS intensity and ratio changes to quantify Zn2+ levels.

Main Results:

• CSZin exhibits a shift in nitrile stretching frequency and increased SRS intensity upon binding Zn2+.
• Successful in vitro detection of Zn2+ ions.
• First demonstration of recognition-based SRS imaging of Zn2+ in live cells.
• Changes in labile Zn2+ pools were observed in normal and tumorigenic cells, correlating with cancer progression.
• CSZin showed response to paramagnetic ions, enabling turn-on detection.

Conclusions:

• CSZin is an effective vibrational probe for Zn2+ detection in biological settings using SRS microscopy.
• This probe enables imaging of dynamic changes in Zn2+ pools in live cells and cancer models.
• The modular design of CSZin holds promise for developing sensors for other metal ions.
• This work expands the chemical toolbox for bioimaging, offering an alternative to fluorescence for challenging species.