Electronic field effect detection of SARS-CoV-2 N-protein before the onset of symptoms.

As part of the efforts to contain the pandemic, researchers around the world have raced to develop testing platforms to detect the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes the Coronavirus disease 2019 (COVID-19). Within the different detection platforms studied, the field effect transistor (FET) is a promising device due to its high sensitivity and fast detection capabilities. In this work, a graphene-based FET which uses a boron and nitrogen co-doped graphene oxide gel (BN-GO gel) transducer functionalized with nucleoprotein antibodies, has been investigated for the detection of SARS-CoV-2 nucleocapsid (N)-protein in buffer. This biosensor was able to detect the viral protein in less than 4 min, with a limit of detection (LOD) as low as 10 ag/mL and a wide linear detection range stretching over 11 orders of magnitude from 10 ag/mL-1 µg/mL. This represents the lowest LOD and widest detection range of any COVID-19 sensor and thus can potentially enable the detection of infected individuals before they become contagious. In addition to its potential use in the COVID-19 pandemic, our device serves as a proof-of-concept of the ability of functionalized BN-GO gel FETs to be used for ultrasensitive yet robust biosensors.

An ultrasensitive heart-failure BNP biosensor using B/N co-doped graphene oxide gel FET.

Heart failure (HF) is the number one cause of death in the world. B-type natriuretic peptide (BNP) is a recognized biomarker for HF and can be used for early detection. Field effect transistor (FET) biosensors have the ability to sense BNP in much shorter times than conventional clinical studies. The lowest limit of detection (LOD) of state-of-the-art HF FET biosensors is 100 fM and detection ranges are short, being less than 4 orders of magnitude. In this work, a B/N co-doped graphene oxide (GO) gel (BN-GO) was used as the channel material in an FET biosensor targeting BNP. The sensor was able to sense BNP in as little as 2 min, with an LOD as low as 10 aM and a wide linear detection range of 10 aM-1 µM, stretching over 11 orders of magnitude. The biosensor showed great selectivity and minimal response towards K+ and OH- ions and the human epidermal growth factor receptor (HER2) protein. This biosensor serves as a proof-of-concept of the ability of BN-GO gel FETs to be used for ultrasensitive biosensors.

Efficient all-optical switching using slow light within a hollow fiber.

We demonstrate a fiber-optical switch that is activated at tiny energies corresponding to a few hundred optical photons per pulse. This is achieved by simultaneously confining both photons and a small laser-cooled ensemble of atoms inside the microscopic hollow core of a single-mode photonic-crystal fiber and using quantum optical techniques for generating slow light propagation and large nonlinear interaction between light beams.

Nonlinear optics with stationary pulses of light.

We show that the recently demonstrated technique for generating stationary pulses of light [M. Bajcsy, A. S. Zibrov, and M. D. Lukin, Nature (London) 426, 638 (2003)] can be extended to localize optical pulses in all three spatial dimensions in a resonant atomic medium. This method can be used to dramatically enhance the nonlinear interaction between weak optical pulses. In particular, we show that an efficient Kerr-like interaction between two pulses can be implemented as a sequence of several purely linear optical processes. The resulting process may enable coherent interactions between single photon pulses.

Stationary pulses of light in an atomic medium.

Physical processes that could facilitate coherent control of light propagation are under active exploration. In addition to their fundamental interest, these efforts are stimulated by practical possibilities, such as the development of a quantum memory for photonic states. Controlled localization and storage of photonic pulses may also allow novel approaches to manipulating of light via enhanced nonlinear optical processes. Recently, electromagnetically induced transparency was used to reduce the group velocity of propagating light pulses and to reversibly map propagating light pulses into stationary spin excitations in atomic media. Here we describe and experimentally demonstrate a technique in which light propagating in a medium of Rb atoms is converted into an excitation with localized, stationary electromagnetic energy, which can be held and released after a controllable interval. Our method creates pulses of light with stationary envelopes bound to an atomic spin coherence, offering new possibilities for photon state manipulation and nonlinear optical processes at low light levels.