Rapid Scan Electron Paramagnetic Resonance using an EPR-on-a-Chip Sensor

Abstract

Abstract. Electron paramagnetic resonance (EPR) spectroscopy is the method of choice to investigate and quantify paramagnetic species in many scientific fields, including materials science and the life sciences. Common EPR spectrometers use electromagnets and microwave (MW) resonators, limiting their application to dedicated lab environments. Here, we present an improved design of a miniaturized EPR spectrometer implemented on a silicon microchip (EPR-on-a-chip, EPRoC). In place of a microwave resonator, EPRoC uses an array of injection-locked voltage-controlled oscillators (VCOs), each incorporating a 200 µm diameter coil, as a combined microwave source and detector. The individual miniaturized VCO elements provide an excellent spin sensitivity reported to be about 4 × 109 spins/√Hz, which is extended by the array over a larger area for improved concentration sensitivity. A striking advantage of this design is the possibility to sweep the MW frequency instead of the magnetic field, which allows the use of smaller, permanent magnets instead of the bulky and power-hungry electromagnets required for field-swept EPR. Here, we report rapid scan EPR (RS-EPRoC) experiments performed by sweeping the frequency of the EPRoC VCO array. RS-EPRoC spectra demonstrate an improved SNR by approximately two orders of magnitude for similar signal acquisition times compared to continuous wave (CW-EPRoC) methods, which may improve the absolute spin and concentration sensitivity of EPR-on-a-Chip at 14 GHz to about 6 × 107 spins/√Hz and 3.6 nM/√Hz, respectively.

Synergies between Hyperpolarized NMR and Microfluidics: A Review

“…Arguably the smallest-scale implementation of Overhauser DNP to date has made use of a single-chip CMOS EPR spectrometer [102]. It has been shown that the circuitry required for EPR spectroscopy can be integrated into a single, high-field compatible complementary metal-oxide semiconductor (CMOS) chip [138][139][140]. Such integrated EPR spectrometers are extremely compact, with chip sizes of only a few millimeters, and can be operated with low power requirements.…”

Synergies between Hyperpolarized NMR and Microfluidics: A Review

“…Arguably the smallest-scale implementation of Overhauser DNP to date has made use of a single-chip CMOS EPR spectrometer [102]. It has been shown that the circuitry required for EPR spectroscopy can be integrated into a single, high-field compatible complementary metal-oxide semiconductor (CMOS) chip [138][139][140]. Such integrated EPR spectrometers are extremely compact, with chip sizes of only a few millimeters, and can be operated with low power requirements.…”