Glucose is the most important analyte for biosensors. Recently a DNA aptamer was reported allowing binding-based detection. However, due to a relatively weak binding affinity, it is difficult to perform binding assays to understand the property of this aptamer. In this work, we replaced the only adenine base in the aptamer binding pocket with a 2-aminopurine (2AP) and used fluorescence spectroscopy to study glucose binding. In the selection buffer, glucose increased the 2AP fluorescence with a K d of 15.0 mM glucose, which was comparable with the 10 mM K d previously reported using the strand displacement assay. The binding required two Na + ions or one Mg 2 + that cannot be replaced by Li + or K + . The binding was weaker at higher temperature and its van't Hoff plot indicated enthalpy-driven binding. While other monosaccharides failed to achieve saturated binding even at high concentrations, two glucosecontaining disaccharides, namely trehalose and sucrose, reached a similar fluorescence level as glucose although with over 10-fold higher K d values. Detection limits in both the selection buffer (0.9 mM) and in artificial interstitial fluids (6.0 mM) were measured.
DNA has been used for directing the growth of noble metal nanoparticles into different morphologies. Most previous studies focused on the effect of DNA sequence, while the effect of DNA adsorption was not thoroughly explored. In this work, we controlled the seeded growth of AuNPs by using the same DNA sequence but under different initial adsorption conditions: room temperature and heating. DNA adsorbed by heating induced more anisotropic nanoparticle growth, and the most effect was observed with 100 nM C30 DNA, where nanoflowers were obtained for the heated sample. By measuring DNA adsorption and desorption, heating did not increase DNA adsorption density but increased the adsorption affinity. The percentage of adsorbed DNA before the growth was only about 10%, regardless of heating, while after the growth, the associated DNA reached 75% or more, indicating that the free DNA also influenced the growth. This study offers fundamental insights into the effect of DNA adsorption on seeded AuNP growth, providing a method to tune the morphology of nanoparticles without changing DNA sequence.
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