Isoelectric characteristics and the secondary structure of some nucleic acids

Lee

et al. 2019

Sci Rep

118

Microenvironment responsive nanomaterials are attractive for therapeutic applications with regional specificity. Here we report pH responsive gold nanoparticles which are designed to aggregate in acidic condition similar to cancer environment and returned to its original disassembled states in a physiological pH. The pH responsive behavior of the particles is derived by change of electrostatic interaction among the particles where attraction and repulsion play a major role in low and high pH of the environment, respectively. Since different electrostatic interaction behavior of the particles in varied pH is induced not by irreversible chemical change but by simple protonation differences, the pH responsive process of assembly and disassembly is totally reversible. The low pH specific aggregation of gold nanoparticles resulted in red shift of plasmonic absorption peak and showed higher photothermal efficacy in acidic pH than in normal physiological pH. The low pH specific photothermal effect with long wave laser irradiation was directly applied to cancer specific photothermal therapy and resulted higher therapeutic effect for melanoma cancer cells than non-pH responsive gold nanoparticles.

Section: Resultsmentioning

confidence: 99%

Reversibly pH-responsive gold nanoparticles and their applications for photothermal cancer therapy

Lee

et al. 2019

Sci Rep

118

“…After this time a stringency rinse using the measuring buffer (10 mM PB, pH 7.4) was performed in order to remove strands that did not hybridize or were weakly bound, and finally the transistor TCs were measured. The isoelectric point of DNA is close to 5.0, 47 therefore, at physiological pH, DNA molecules are negatively charged. The electrostatic field of these charges immobilized near the graphene surface will induce, by local gating, p-doping, which shifts V Dirac to more positive V GS .…”

Section: Dna Biosensor Performancementioning

confidence: 99%

Attomolar Label-Free Detection of DNA Hybridization with Electrolyte-Gated Graphene Field-Effect Transistors

et al. 2019

In this work, we develop a field-effect transistor with a two-dimensional channel made of a single graphene layer to achieve label-free detection of DNA hybridization down to attomolar concentration, while being able to discriminate a single nucleotide polymorphism (SNP). The SNP-level target specificity is achieved by immobilization of probe DNA on the graphene surface through a pyrene-derivative heterobifunctional linker. Biorecognition events result in a positive gate voltage shift of the graphene charge neutrality point. The graphene transistor biosensor displays a sensitivity of 24 mV/dec with a detection limit of 25 aM: the lowest target DNA concentration for which the sensor can discriminate between a perfect-match target sequence and SNP-containing one.

“…Although the

1 / f

noise did not appreciably change up to pH ∼8, it is important to strike a balance between analyte responsiveness and solution pH. For example, the isoelectric point (

p I

) of DNA (although base‐pair composition‐dependent) is generally around ∼5 [45]. Therefore, even though the

1 / f

noise is low at pH ∼5, the net charge of DNA would be close to zero, resulting into a small EPF imparted on it.…”

Section: Resultsmentioning

confidence: 99%

Assessment of 1/f noise associated with nanopores fabricated through chemically tuned controlled dielectric breakdown

et al. 2021

Recently, we developed a fabrication method—chemically‐tuned controlled dielectric breakdown (CT‐CDB)—that produces nanopores (through thin silicon nitride membranes) surpassing legacy drawbacks associated with solid‐state nanopores (SSNs). However, the noise characteristics of CT‐CDB nanopores are largely unexplored. In this work, we investigated the 1/f noise of CT‐CDB nanopores of varying solution pH, electrolyte type, electrolyte concentration, applied voltage, and pore diameter. Our findings indicate that the bulk Hooge parameter (αb) is about an order of magnitude greater than SSNs fabricated by transmission electron microscopy (TEM) while the surface Hooge parameter (αs) is ∼3 order magnitude greater. Theαs of CT‐CDB nanopores was ∼5 orders of magnitude greater than theirαb, which suggests that the surface contribution plays a dominant role in 1/f noise. Experiments with DNA exhibited increasing capture rates with pH up to pH ∼8 followed by a drop at pH ∼9 perhaps due to the onset of electroosmotic force acting against the electrophoretic force. The1/f noise was also measured for several electrolytes and LiCl was found to outperform NaCl, KCl, RbCl, and CsCl. The 1/f noise was found to increase with the increasing electrolyte concentration and pore diameter. Taken together, the findings of this work suggest the pH approximate 7–8 range to be optimal for DNA sensing with CT‐CDB nanopores.