Microfluidic quantum sensing platform for lab-on-a-chip applications

Abstract

Lab-on-a-chip (LOC) applications have emerged as an invaluable tools in physical and life sciences. However, LOC applications require extensive sensor miniaturization to leverage their full potential. In recent years, novel atom-sized quantum sensors have enabled measurements of temperature, electric and magnetic fields on the nano- to microscale. Nevertheless, the technical complexity of both disciplines has so far impeded an uncompromising combination of LOC and quantum sensors. Here, we present a fully integrated microfluidic platform for solid-state spin quantum sensors, such as the nitrogen-vacancy (NV) center in diamond. Our platform fulfills all technical requirements, such as fast spin manipulation, enabling full quantum sensing capabilities, biocompatibility, and easy adaptability to arbitrary channel and chip geometries. To illustrate the vast potential of quantum sensors in LOC devices, we demonstrate various NV center-based magnetic resonance experiments for chemical analysis in our microfluidic platform. We anticipate our microfluidic quantum sensing platform as a novel tool for electrochemistry, high throughput reaction screening, bioanalytics or organ-on-a-chip, and single-cell studies.

Sensing Diamagnetic Electrolytes with Spin Defects in Diamond

“…T 1 Relaxometry on Electrolytes with Near-Surface NV-Center Ensembles In this study we use near-surface high dense NV-center ensembles (implanted with 15 N at an energy of 2.5 keV and a fluence of 2 × 10 12 cm −2 ), distributed ∼ 5 nm underneath the diamond surface, 13,36,37 to investigate the effect of aqueous electrolyte solutions on the spinlattice relaxation time T 1 probed by NV-relaxometry. Before experiments are conducted, we prepare the diamond surface with a tri-acid clean procedure according to Brown et al 38 This procedure not only ensures to remove non-diamond carbon material from the interface but also creates an oxygen-terminated surface comprised of mixed carbon oxide species including hydroxyl groups, ethers, ketones, aldehydes and carboxylic acids.…”

“…39 We position the diamond in a microfluidic device that guarantees controllable in-and output of the applied liquids, prevents sample evaporation and provides a constant and defined volume for following measurements (see Figure 1a). 15 Importantly, the microfluidic device avoids a direct contact between the liquid and the microwave delivery.…”

“…Two 2 × 2 × 0.5 mm electronic grade diamond samples (natural 13 C abundance, Element Six) were implanted with 15 N at an energy of 2.5 keV or 4 keV, an off-axis tilt of 7°and a fluence of 2 × 10 12 cm −2 by Innovion and annealed according to Bucher et al 18 Before experiments are conducted, the diamonds are cleaned with a tri-acid cleaning protocol according to Brown et al: 38 Samples are boiled in equal parts of sulfuric, nitric and perchloric acid at a temperature of 280 °C for two hours. This cleaning procedure is also applied before the deposition of aluminium oxide (Al 2 O 3 ) on the diamond.…”

“…9,10 This unprecedented sensitivity is achieved due to the atomic size of the qubit enabling its location only a few nanometer away from the diamond interface (see Figure 1a). 11 Near surface NV-centers (≤ 20 nm below the surface) can be used to sense nuclear magnetic resonance (NMR) 8,[12][13][14][15] and electron spin resonance (ESR) signals 16 from nanoscale chemical and biological samples. The NV-center translates these magnetic field fluctuations directly to an optical signal, detected by a change in the fluorescence intensity.…”

“…Together with optical spin state initialization with green laser light and coherent spin state manipulation with microwave pulses, these key features make the NV-center a unique tool for (bio)chemical analysis. 11,15,17,18 NV-centers are also perceptive to electric fields. 4,19 Even a single elementary charge located ∼ 150 nm away from the quantum sensor produces a strong enough static electric field to affect an NV-center's ODMR (optically detected magnetic resonance) transitions.…”