3 research outputs found
Femtomolar detection of the heart failure biomarker NT-proBNP in artificial saliva using an immersible liquid-gated aptasensor with reduced graphene oxide
Measuring NT-proBNP biomarker is recommended for preliminary diagnostics of
the heart failure. Recent studies suggest a possibility of early screening of
biomarkers in saliva for non-invasive identification of cardiac diseases at the
point-of-care. However, NT-proBNP concentrations in saliva can be thousand time
lower than in blood plasma, going down to pg/mL level. To reach this level, we
developed a label-free aptasensor based on a liquid-gated field effect
transistor using a film of reduced graphene oxide monolayer (rGO-FET) with
immobilized NT-proBNP specific aptamer. We found that, depending on ionic
strength of tested solutions, there were different levels of correlation in
responses of electrical parameters of the rGO-FET aptasensor, namely, the Dirac
point shift and transconductance change. The correlation in response to
NT-proBNP was high for 1.6 mM phosphate-buffered saline (PBS) and zero for 16
mM PBS in a wide range of analyte concentrations, varied from 1 fg/mL to 10
ng/mL. The effects of transconductance and Dirac point shift in PBS solutions
of different concentrations are discussed. The biosensor exhibited a high
sensitivity for both transconductance (2 uS/decade) and Dirac point shift (2.3
mV/decade) in diluted PBS with the linear range from 10 fg/mL to 1 pg/mL. The
aptasensor performance has been also demonstrated in undiluted artificial
saliva with the achieved limit of detection down to 41 fg/mL (~4.6 fM)
Common origin of quasi-periodic pulsations in microwave and decimetric solar radio bursts
We analyse quasi-periodic pulsations (QPP) detected in the microwave and decimetre radio emission of the 5 May 2017 7:04 UT (SOL2017-09-05T07:04) solar flare, using simultaneous observations by the Siberian Radioheliograph 48 (SRH-48, 4βββ8 GHz) and Mingantu Spectral Radioheliograph (MUSER-I, 0.4βββ2 GHz). The microwave emission was broadband with a typical gyrosynchrotron spectrum, while a quasi-periodic enhancement of the decimetric emission appeared in a narrow spectral band (500βββ700 MHz), consistent with the coherent-plasma-emission mechanism. The periodicity that we found in microwaves is about 30 seconds, coming from a compact loop-like source with a typical height of about 31 Mm. The decimetric emission exhibited a periodicity of about 6 seconds. We suggest a qualitative scenario linking the QPPs observed in both incoherent and coherent spectral bands and their generation mechanisms. The properties of the QPPs found in the microwave signal are typical for perturbations of the flare loop by the standing sausage mode of a fast magnetohydrodynamic (MHD) wave. Our analysis indicated that this sausage-oscillating flare loop was the primary source of oscillations in the discussed event. The suggested scenario is that a fundamental sausage harmonic is the dominant cause for the observed QPPs in the microwave emission. The initiation of oscillations in the decimetric emission is caused by the third sausage harmonic via periodic and nonlinear triggering of the acceleration processes in the current sheets, formed at the interface between the sausage-oscillating flare loop and the external coronal loop that extended to higher altitudes. Our results demonstrate the possible role of MHD wave processes in the release and transport of energy during solar flares, linking coherent and incoherent radio emission mechanisms