Electrolyte Detection by Ion Beam Analysis, in Continuous Glucose Sensors and in Microliters of Blood using a Homogeneous Thin Solid Film of Blood, HemaDrop™

Percolation of blood and of interstitial fluids into implantable continuous glucose sensors (CGS) for diabetics presently limits sensor lifetime between 3 and 7 days. Na⁺ mobile ions in body fluids damage Si-based CGS sensors electronics. The direct detection of Na percolation is investigated by Ion Beam Analysis (IBA) and Proton Induced X-ray Emission (PIXE) in previously used CGS. Based on these results, a new technology called HemaDrop^TM is then tested to prepare small volume (5-10 μL) of blood for IBA. A species's detectability by IBA scales with the square of the ratio of element's atomic number Z to that of the substrate. Because Na has a low atomic number (Z=11), Si signals from sensor substrates can prevent Na detection in Si by 2 mega electron volt (MeV) IBA. Using 4.7 MeV ²³Na (α, α)²³Na nuclear resonance (NR) can increase the ²³Na scattering cross section and thus its detectability in Si. The NR energy, width, and resonance factor, is calibrated via two well-known alpha (α) particle signals with narrow energy spreads: a 5.486 ± 0.007 MeV ²⁴¹Am α-source (ΔE = 0.12%) and the 3.038 ± 0.003 MeV ¹⁶O(α, α)¹⁶O NR (ΔE = 0.1%). Next, the NR cross section is calibrated via 100 nm NaF thin films on Si(100) by scanning the beam energy. The²³Na (α, α) NR energy is found to be 4.696 ± 0.180 MeV, and the NR/RBS cross section 141 ± 7%. This is statistically significant but small compared to the 4.265 MeV ¹²C NR (1700%) and 3.038 MeV ¹⁶O NR (210%), and insufficient to detect small amounts of ²³Na in Si. Next, a new method of sample preparation HemaDrop^TM, is tested for detection of elements in blood, such Fe, Ca, Na, Cl, S, K, C, N, and O, as an alternative to track fluid percolation and Na diffusion in damaged sensors. Detecting more abundant, heavier elements in blood and interstitial fluids can better track fluid percolation and Na⁺ ions in sensors. Both Na detection and accuracy of measured blood composition by IBA is greatly improved by using HemaDrop^TM sample preparation to create Homogeneous Thin Solid Films (HTSFs) of blood from 5-10 μL on most substrates. HTSF can be used in vacuo such as 10^-8 -10^-6 Torr).