Devices for blood sampling and DNA sensing

ABDULLA AL MAMUN

doi:10.7273/000005046

Microneedles for blood sampling are getting more and more attention in research and commercialization since their advancement in the 1990s due to the advantages over traditional hypodermic needles such as minimum invasiveness, low material and fabrication cost, and precise needle geometry control, etc. The design and fabrication of microneedles depend on various factors such as the type of materials used, fabrication planes and techniques, needle structures, etc. In the past years, in-plane and out‐of‐plane microneedle technologies made by silicon (Si), polymer, metal, and other materials have been developed for numerous biomedical applications including drug delivery, sample collections, medical diagnostics, and bio‐sensing. Among these microneedle technologies, in‐plane Si microneedles excel by the inherent properties of Si such as mechanical strength, wear resistance, biocompatibility, and structural advantages of in‐plane configuration such as a wide range of length, readiness of integration with other supporting components, and complementary metal‐oxide‐semiconductor (CMOS) compatible fabrication. The aim of this microneedle research is twofold. Firstly, to provide a review of in‐plane Si microneedles with a focus on fabrication techniques, theoretical and numerical analysis, experimental characterization of structural and fluidic behaviors, major applications, potential challenges, and future prospects. Secondly, to investigate the eleven design of microneedles by post-complementary metal-oxide-semiconductor (CMOS) compatible microfabrication processes and to character them via pricking tests by insertion in chicken breast flesh. Mechanical strength of all designs was also evaluated by theoretical calculation and finite element modeling (FEM) for bending and buckling analysis. To efficiently improve the sharpness and insertion, the wedge-shaped needle tips with thickness determined by Si wafer thickness were sharpened by a wet chemical etching process. Insertion forces recorded from pricking tests and bending and buckling from theoretical calculation and FEM analysis before and after etching were compared. The results showed that the insertion force, free bending force and the maximum buckling force were all reduced and the maximum bending stress were improved after tip sharpening. Furthermore, the buckling safety factor of all eleven designs was greater than 1 (one) and the maximum bending stress was less than the fracture strength of Si, indicating that our in-plane Si microneedles are robust enough for insertion into human skin. Besides blood sampling, DNA sensing is also critical in various applications such as the early diagnosis of diseases, investigation of forensic evidence, food processing, agriculture, environmental protection, etc. As a wide bandgap semiconductor with excellent chemical, physical, electrical and biocompatible properties, SiC is a promising material for DNA sensors. In recent years, a variety of SiC based DNA sensors have been reported, such as nanoparticles and quantum dots, nanowire, nanopillar, and nanowire-based field-effect-transistor (FET), etc. In addition to microneedle research for blood sampling, this thesis aims to provide a brief review with focus on the major SiC based DNA sensing technologies, functions, and testing results. Our recently developed planar 4H-SiC chemiresistor for label free DNA sensing with a sensitivity of 100 aM is also reported.

Devices for blood sampling and DNA sensing

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