Using a fluorescence quenching method to detect DNA adsorption onto single-walled carbon nanotube surfaces

An efficient method to quantitatively detect competitive adsorption of DNA on single-walled carbon nanotube surfaces

In this study, we quantitatively detected adsorption and desorption of DNA molecules that competed with sodium cholate (SC) molecules on single-walled carbon nanotubes (SWNTs) by fluorescence spectroscopy. In previous studies, competitive adsorption and/or replacement were studied based on techniques such as near-infrared (NIR) absorbance and photoluminescence (PL) spectroscopy of SWNTs. In those studies, adsorption of organic molecules was detected as spectral changes in SWNTs, but not in organic molecules. In this study, we employed fluorescent-labeled DNA (Fc-DNA) to detect competitive adsorption through quenching of fluorescent dyes that were attached to DNA molecules. Through this approach, the adsorption behaviors of DNA molecules could be directly determined. Hence, we found that Fc-DNA molecules adsorbed on SWNT surfaces that were pre-wrapped with SC when the SC concentration was reduced. However, when SC concentrations recovered after three days of incubation, detachment of Fc-DNA molecules was observed. In addition, our method could be applied to evaluate the adsorption of fluorescent dyes on SWNT surfaces instead of DNA molecules. Hence, our method is effective in studying competitive adsorption of organic molecules on SWNT surfaces. The obtained information is complementary to that obtained from NIR spectroscopy of SWNTs.

Corona Exchange Dynamics on Carbon Nanotubes by Multiplexed Fluorescence Monitoring

Noncovalent adsorption of DNA on nanoparticles has led to their widespread implementation as gene delivery tools and optical probes. Yet, the behavior and stability of DNA-nanoparticle complexes once applied in biomolecule-rich, in vivo environments remains unpredictable, whereby biocompatibility testing usually occurs in serum. Here, we demonstrate time-resolved measurements of exchange dynamics between solution-phase and adsorbed corona-phase DNA and protein biomolecules on single-walled carbon nanotubes (SWCNTs). We capture real-time binding of fluorophore-labeled biomolecules, utilizing the SWCNT surface as a fluorescence quencher, and apply this corona exchange assay to study protein corona dynamics on ssDNA-SWCNT-based dopamine sensors. We study exchange of two blood proteins, albumin and fibrinogen, adsorbing to and competitively displacing (GT)6 vs (GT)15 ssDNA from ssDNA-SWCNTs. We find that (GT)15 binds to SWCNTs with a higher affinity than (GT)6 and that fibrinogen interacts with ssDNA-SWCNTs more strongly than albumin. Albumin and fibrinogen cause a 52.2% and 78.2% attenuation of the dopamine nanosensor response, coinciding with 0.5% and 3.7% desorption of (GT)6, respectively. Concurrently, the total surface-adsorbed fibrinogen mass is 168% greater than that of albumin. Binding profiles are fit to a competitive surface exchange model which recapitulates the experimental observation that fibrinogen has a higher affinity for SWCNTs than albumin, with a fibrinogen on-rate constant 1.61-fold greater and an off-rate constant 0.563-fold smaller than that of albumin. Our methodology presents a generic route to assess real-time corona exchange on nanoparticles in solution phase and more broadly motivates testing of nanoparticle-based technologies in blood plasma rather than the more ubiquitously tested serum conditions.

Quantitative Detection of the Disappearance of the Antioxidant Ability of Catechin by Near-Infrared Absorption and Near-Infrared Photoluminescence Spectra of Single-Walled Carbon Nanotubes

We succeeded in quantitatively detecting the disappearance of catechin antioxidant ability as a function of time using near-infrared (NIR) absorbance and NIR photoluminescence (PL) spectra of single-walled carbon nanotubes (SWNTs) wrapped with DNA molecules (DNA-SWNT hybrids). When 15 μg/mL of catechin was added to the oxidized hybrid suspension, the absorbance of SWNTs increased, according to the antioxidant ability of catechin, and the effect was maintained at least for 30 min. When catechin concentrations were less than 0.3 μg/mL, SWNT absorbance gradually decreased, although it increased when catechin is added. The results revealed that disappearance of the catechin effects could be quantitatively detected by NIR absorbance spectra. When NIR PL was employed, the disappearance of PL intensity was also observed in the case of low catechin concentrations. However, time-lapse measurement of the disappearance was difficult because the PL intensity was rapidly quenched. In addition, the optical responses were different due to different chirality of SWNTs. Our results suggested that both NIR absorbance and PL can detect disappearance of catechin antioxidant effects; in particular, slow response of NIR absorbance was effective to detect time dependence of the disappearance of the catechin effects. Contrarily, PL revealed huge and rapid responses in contrast to NIR absorbance. PL might be effective for reversible use of DNA-SWNT hybrids as a nanobiosensor.

Luminescent switch sensors for the detection of biomolecules based on metal-organic frameworks

Metal-organic frameworks (MOFs) as sensing materials have experienced explosive growth in recent years due to their intrinsic merits, such as structural diversity, high porosity, large surface area, extraordinary adsorption affinities, etc. Biomolecules such as DNA, protein, and vitamins play vital roles in metabolism. Moreover, the sensitive detection of biomolecules is of importance in the disease prevention and treatment. This review intends to provide an update on the recent progress in the detection of various biomolecules via MOF-based luminescent sensors. MOFs are successful in the detection of DNA, RNA, protein, and other biomolecules. MOF-based luminescent sensors function by utilizing different mechanisms, including luminescent responses of enhancement and quenching, which are defined as "turn-on" and "turn-off" responses, respectively. Then, a short comparison of the "turn-on" and "turn-off" types of sensors is also made.