Helical Assembly of Flavin Mononucleotides on Carbon Nanotubes as Multimodal Near-IR Hg(II)-Selective Probes

Abstract

The development of novel methods to detect mercury is of paramount importance owing to the impact of this metal on human health and the environment. We observed that flavin mononucleotide (FMN) and its helical assembly with a single-walled carbon nanotube (SWNT) selectively bind Hg2+ arising from HgCl2 and MeHgCl. Absorption spectroscopic studies show that FMN preferentially forms a 2:1 rather than a 1:1 complex with Hg2+ at high FMN concentrations. On the basis of the analogy to the thymine–Hg–thymine complex, it is proposed that the 2:1 complex between FMN and Hg2+ comprises a Hg-bridged pair of FMN groups, regardless of the presence of SWNT. Upon addition of as little as a few hundred nanomoles of Hg2+, both FMN and FMN–SWNT exhibit absorption and photoluminescence (PL) changes. Moreover, FMN–SWNT displays simultaneous multiple sigmoidal changes in PL of SWNT tubes having different chiral vectors. Assessment of binding affinities using the Hill equation suggests that 2:1 and 1:1 complexes form between Hg2+ and FMN groups on the FMN–SWNT. Theoretical calculations indicate that optical changes of the FMN–SWNT originate from Hg-mediated conformational changes occurring on the helical array of FMN on the SWNT. High-resolution transmission electron microscopy revealed that the presence of Hg2+ in complexes with the FMN–SWNT enables visualization of helical periodic undulation of FMN groups along SWNT without the need for staining. Circular dichroism (CD) study revealed that FMN–SWNT whose CD signal mainly originates from FMN decreases dichroic bands upon the addition of Hg2+ owing to the formation of a centrosymmetric FMN–Hg–FMN triad on SWNT. The binding mode specificity and multimodal changes observed in response to Hg2+ ions suggest that systems based on FMN–SWNT can serve as in vivo NIR beacons for the detection of various mercury derivatives.

Recent Advances in Structure Separation of Single‐Wall Carbon Nanotubes and Their Application in Optics, Electronics, and Optoelectronics

“…[128] The formation of a helical ribbon of flavin mononucleotide (FMN) around nanotubes was attributed to the cooperative hydrogen bonding between adjacent flavin moieties under concentric 𝜋-𝜋 interactions with nanotube surfaces. [128] Although the nucleotides have demonstrated certain ability for the structure recognition of SWCNTs in subsequent studies, [129,[158][159][160][161] their efficiencies for dispersion and separation are still limited, compared with the widely used ssDNA and conjugated polymers mentioned above.…”

“…[129,363] Paradimitrakopoulos and Ju et al found that FMN containing a chiral D-ribityl phosphate chain with a right-handed helix can wrap around nanotubes in a helical pattern depending on the chirality and handedness of the SWCNTs. [128,129,158,159,364] In addition, Nakashima et al designed and synthesized copolymers composed of PFO and chiral binaphthol moieties for the enantiomer separation of (6, 5) and (7, 5) SWCNTs (Figure 19c). [363] Most recently, Xu et al synthesized an chiral polyfluorene that can be cleaved by acid; this polyfluorene exhibits strong recognition for SWCNT enantiomers through simple bath sonication and centrifugation (Figure 19d).…”

“…found that FMN containing a chiral D‐ribityl phosphate chain with a right‐handed helix can wrap around nanotubes in a helical pattern depending on the chirality and handedness of the SWCNTs. [ 128,129,158,159,364 ] In addition, Nakashima et al. designed and synthesized copolymers composed of PFO and chiral binaphthol moieties for the enantiomer separation of (6, 5) and (7, 5) SWCNTs (Figure 19c).…”

Rapid Determination of Mercury Ions in Environmental Water Based on an N-Rich Covalent Organic Framework Potential Sensor

“…e ion-selective electrode (ISE) method, as a rapid analytical tool, has been widely developed in the elds of the environment, medicine, and agriculture due to its advantages of fast speed, simple preparation, low cost, and high sensitivity [11]. In the process of preparing ion-carrier membranes with di erent selective electrodes, many organic, and inorganic complexes can be used as selective carriers of Mercury ions, such as crown ether [12], amide [13], glycidyl diamine [14], metalloporphyrin [15], Schi base [16], calixarene derivatives [17,18], and alkylamine Mercury salt complexes [19]. erefore, there is an urgent need to prepare Mercury ion-selective electrodes with good selectivity and a low detection limit.…”

Moiré patterns and carbon nanotube sorting

“…Widely applied for the nanotubes sorting flavin mononucleotide (FMN), as is known, can form a dense double-row coating both on some SWCNTs and on planar graphene [31][32][33][34][35][36]. Here, using this experimental fact, we first reduce the geometric conditions for successful formation of the coating (and, therefore, successful sorting of SWCNTs by these molecules) to an analysis of commensurability and geometric characteristics of MPs appearing between layers of a specific virtual bilayer nanotube.…”