Strongly Bound Sodium Dodecyl Sulfate Surrounding Single-Wall Carbon Nanotubes

Abstract

NMR techniques have been widely used to infer molecular structure, including surfactant aggregation. A combination of optical spectroscopy, proton NMR spectroscopy, and pulsed field gradient NMR (PFG NMR) is used to study the adsorption number for sodium dodecyl sulfate (SDS) with single-wall carbon nanotubes (SWCNTs). Distinct transitions in the NMR chemical shift of SDS are observed in the presence of SWCNTs. These transitions demonstrate that micelle formation is delayed by SWCNTs due to the adsorption of SDS on the nanotube surface. Once the nanotube surface is saturated, the free SDS concentration increases until micelle formation is observed. Therefore, the adsorption number of SDS on SWCNTs can be determined by the changes to the apparent critical micelle concentration (CMC). PFG NMR found that SDS remains strongly bound onto the nanotube. Quantitative analysis of the diffusivity of SDS allowed calculation of the adsorption number of strongly bound SDS on SWCNTs. The adsorption numbers from these techniques give the same values within experimental error, indicating that a significant fraction of the SDS interacting with nanotubes remains strongly bound for as long as 0.5 s, which is the maximum diffusion time used in the PFG NMR measurements.

Overcoming Surfactant-Induced Morphology Instability of Noncrosslinked Diblock Copolymer Nano-Objects Obtained by RAFT Emulsion Polymerization

“…Furthermore, at ambient temperature, fbound also decreased at the SDS concentration of 10 mg ml -1 (well above the critical micellization concentration of SDS -2.5 mg mL -1 ) 38 indicating that a large portion of added SDS molecules tended to form SDS aggregates (with alkyl groups as the core and sulfate groups as the shell) rather than co-assembly with P(DEGMA29-co-HPMA6) chains. 46 Altogether, the data obtained from the PFG-NMR supported our hypothesis that a limited amount of added SDS binds to P(DEGMA29-co-HPMA6) chains, thus leading to the surfactant tolerance of noncrosslinked nanoparticles made from P(DEGMA-co-HPMA) macro-CTA. Further, the nature of the binding between SDS and P(DEGMA-co-HPMA) is dynamic and sensitive to both temperature and SDS concentration.…”

“…This result is consistent with the partial dissociation of SDS/P­(DEGMA 29 - co -HPMA 6 ) at elevated temperature observed in the NOESY NMR results while the observation of bound SDS explains the stabilization of P­(DEGMA 29 - co -HPMA 6 ) particles formed at high temperature prior to and during the emulsion polymerization. Furthermore, at ambient temperature, f bound also decreased at the SDS concentration of 10 mg mL –1 (well above the critical micellization concentration of SDS, 2.5 mg mL –1 ), indicating that a large portion of added SDS molecules tended to form SDS aggregates (with alkyl groups as the core and sulfate groups as the shell) rather than coassembly with P­(DEGMA 29 - co -HPMA 6 ) chains . Altogether, the data obtained from the PFG-NMR supported our hypothesis that a limited amount of added SDS binds to P­(DEGMA 29 - co -HPMA 6 ) chains, thus leading to the surfactant tolerance of noncrosslinked nanoparticles made from P­(DEGMA- co -HPMA) macro-CTA.…”

HIV Detection via a Carbon Nanotube RNA Sensor

“…We base this hypothesis on previous works showing that SDS can be used to suspend carbon nanotubes, 11 due to hydrophobic interactions between the nanotube surface and the 12-carbon-long alkyl chain. 20 We first tested whether SDS would change the baseline emission of the GT 15 miR19 sensor. Dilutions ranging from 0.1% to 1 wt %/vol SDS showed no significant changes in emission wavelength (Figure S2a) or intensity (Figure S2b).…”

“…In an attempt to reduce this apparent FBS-induced fouling of the sensor, we hypothesized that an anionic detergent, sodium dodecyl sulfate (SDS), may associate with bare regions of the nanotube and block nonspecific binding of serum components. We base this hypothesis on previous works showing that SDS can be used to suspend carbon nanotubes, due to hydrophobic interactions between the nanotube surface and the 12-carbon-long alkyl chain . We first tested whether SDS would change the baseline emission of the GT 15 miR19 sensor.…”

Non-covalent Methods of Engineering Optical Sensors Based on Single-Walled Carbon Nanotubes

“…This formation of hemimicellar aggregates on the surface of the SWCNTs typically involves adsorption of the surfactant onto the nanotube followed by the self-assembly of the molecules, which is enabled by diffusion along the nanotube surface (Vo et al, 2016). In contrast, the former, random adsorption of the surfactant on the SWCNT surface, is adopted by weakly amphiphilic molecules [such as flavin mononucleotides (FMN)] and bile acid surfactants (including SC and SDOC) where adsorption is competitive, i.e., follows a Langmuir isotherm (Angelikopoulos and Bock, 2010, 2012; Tummala et al, 2010; Bergler et al, 2016; Xu et al, 2017).…”