Research – Patterson

Single molecule analytics

The ideal nano-analytic tool could definitively identify the exact form of a molecule, including chirality, from the smallest possible sample – a single molecule. We are working to extend our recently developed Single Molecule Inelastic Recoil Spectroscopy to include chiral sensitivity. The resulting tool will be able to quickly and unambiguously identify the isomer, isotopomer, and stereoisomer of a single gas-phase analyte molecule. Additional to its use as a precise chemical analytics tool, our research also serves as a platform for tests of fundamental physics including parity violation in the electroweak force.

Inelastic Recoil Spectroscopy (IRS) is a non-destructive, rotationally resolved spectroscopic method capable of producing high resolution spectra of individual polyatomic molecular ions. Utilizing a laser-cooled, mixed-species Coulomb crystal in a cryogenic ion trap, IRS achieves single-molecule sensitivity comparable to quantum logic spectroscopy (QLS), but overcomes QLS’s current limitation to diatomic species and enables broad applicability to complex polyatomic ions.

a) A molecular ion is co-trapped and sympathetically cooled with a laser-cooled Sr⁺. The ions are confined radially in a linear quadrupole and axially by two endcaps. A constant oscillating voltage (tickle) is applied to an endcap at the Sr⁺ secular frequency. Upon ro-vibrational excitation by a mid-IR source and subsequent inelastic collision, the molecular ion is ejected from the Coulomb crystal but still remains in the trap.

b) The Sr⁺ motion is amplified by the now-on-resonance tickle and the fluorescence is modulated at the secular frequency.

c) The molecular ion eventually re-cools into the crystallized configuration. The fluorescence modulation drops and the measurement is repeated. A lock-in amplifier detects the Sr⁺ fluorescence modulation.

Left: the first ever single molecule resolved spectra of a polyatomic molecule using our previous method of tagging spectroscopy (Tropylium).
Right: Resolved rotational lines found using IRS which has 10,000 ⨉ higher resolution to reveal rotational states of our molecules.

For additional information on this experiment and older generations, see this page.

Microwave three-wave mixing

Chiral molecules exhibit handedness, a fundamental property with significant implications in chemistry, biology, and pharmacology. The differentiation of enantiomers—molecules that are mirror images of each other—remains a critical challenge in analytical chemistry. Conventional methods for chiral analysis often require derivatization or indirect approaches that can introduce inaccuracies or complexities.

Carefully chosen microwave fields with x, y, and z polarization can selectivity excite S- or R- molecules into a target state. Our inelastic recoil will then readout the target state to determine the enantiomer.

Rotational spectroscopy combined with microwave three-wave mixing (M3WM) offers a powerful, non-destructive method for distinguishing molecular enantiomers in the gas phase. This approach provides high-resolution structural information and enables direct chiral discrimination without the need for chemical modifications. The study of 4-mercaptostyrene using these techniques serves as a key demonstration of their applicability to increasingly complex chiral molecules, expanding the toolkit for precision spectroscopy and molecular analysis.

The ability to probe chiral molecules with high sensitivity and resolution has broad implications for fields such as pharmaceutical development, environmental monitoring, and fundamental physics. The integration of rotational spectroscopy and M3WM represents a significant advancement toward more precise and reliable methods for enantiomer differentiation, enhancing our understanding of molecular structures and interactions.

To read more about our experiments using M3WM click here!