Noncovalent Protein and Peptide Functionalization of Single-Walled Carbon Nanotubes for Biodelivery and Optical Sensing Applications

Abstract

ABSTRACT:The exquisite structural and optical characteristics of single-walled carbon nanotubes (SWCNTs), combined with the tunable specificities of proteins and peptides, can be exploited to strongly benefit technologies with applications in fields ranging from biomedicine to industrial biocatalysis. The key to exploiting the synergism of these materials is designing protein/peptide-SWCNT conjugation schemes that preserve biomolecule activity while keeping the near-infrared optical and electronic properties of SWCNTs intact. Since sp 2 bondbreaking disrupts the optoelectronic properties of SWCNTs, noncovalent conjugation strategies are needed to interface biomolecules to the nanotube surface for optical biosensing and delivery applications. An underlying understanding of the forces contributing to protein and peptide interaction with the nanotube is thus necessary to identify the appropriate conjugation design rules for specific applications. This article explores the molecular interactions that govern the adsorption of peptides and proteins on SWCNT surfaces, elucidating contributions from individual amino acids as well as secondary and tertiary protein structure and conformation. Various noncovalent conjugation strategies for immobilizing peptides, homopolypeptides, and soluble and membrane proteins on SWCNT surfaces are presented, highlighting studies focused on developing near-infrared optical sensors and molecular scaffolds for self-assembly and biochemical analysis. The analysis presented herein suggests that though direct adsorption of proteins and peptides onto SWCNTs can be principally applied to drug and gene delivery, in vivo imaging and targeting, or cancer therapy, nondirect conjugation strategies using artificial or natural membranes, polymers, or linker molecules are often better suited for biosensing applications that require conservation of biomolecular functionality or precise control of the biomolecule's orientation. These design rules are intended to provide the reader with a rational approach to engineering biomolecule-SWCNT platforms, broadening the breadth and accessibility of both wild-type and engineered biomolecules for SWCNT-based applications.

Oligonucleotide Length Determines Intracellular Stability of DNA-Wrapped Carbon Nanotubes

“…We employed NIR hyperspectral fluorescence microscopy to assess the chirality-resolved intracellular stability of the (GT)n-SWCNTs [15]. Using a 730 nm excitation laser, we were able to resolve four distinct bands in the NIR region corresponding to the emission spectra of the four brightest SWCNT chiralities, (10,2), (9,4), (8,6), and (8,7) ( Fig. S1a,b) [15].…”

“…Their electronic band gap energies are dependent on their chiral identity, denoted by integers (n,m), and vary based on diameter and rollup angle [4], resulting in semiconducting species which exhibit band gap photoluminescence [3]. Although highly hydrophobic in their raw as-produced form, non-covalent functionalization of SWCNTs using surfactants [5,6] or amphiphilic biomolecules [7][8][9] has been shown to effectively disperse SWCNTs into aqueous solutions while preserving their intrinsic optical properties. Single-stranded DNA can non-covalently functionalize SWCNTs via -stacking of hydrophobic bases onto the SWCNT sidewall, while the hydrophilic phosphate backbone allows for significantly enhanced aqueous solubility [10].…”

Screening of bacteria-binding peptides and one-pot ZnO surface modification for bacterial cell entrapment

“…[3][4][5] Various peptides with these unique characteristics enabling them to bind to specic materials are used as non-covalently bound linkers for material surface modication. 6,7 In addition to their usage for material surface modications, peptides can bind to various targets including bacterial cells. Because of increasing worldwide concerns about pathogenic bacteria, particularly drug-resistant bacteria, bacterial recognition probes are gaining attention as tools for microbial detection.…”

Nanobody‐Conjugated Nanotubes for Targeted Near‐Infrared In Vivo Imaging and Sensing

“…Here,finetuning of the experimental parameters is crucial to prevent colloidal instability resulting from the conjugation of too many nanobodies to the SWCNT surface.T his colloidal stability is ak nown and important, but still often neglected factor in research on peptide-or protein-modified SWCNTs. [24] Using the optimized GBP/SWCNT-(GT) 20 ratio,t he conjugates were still stable even after more than six weeks of storage at 4 8 8C( see Figure S3). Figure 1b shows the retained nIR fluorescence properties after conjugation of the GFP-binding nanobody upon excitation at 561 nm compared to the unconjugated sample.T oprove the successful conjugation of GBP (4)t ot he SWCNT,w ee mployed DNA-and protein-stained sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) ( Figure 1c).…”

“…GFP is av aluable target because al arge number of transgenic organisms and cells are available with GFP-tagged proteins. Noncovalent functionalization is used in order not to alter or destroy the nIR fluorescence of SWCNTs, [21][22][23][24][25] although recently Setaro et al also reported ac ovalent modification strategy preserving the nIR fluorescence. [26] While there are many different noncovalent functionalization concepts available, [21,27,28] DNA/SWCNTs have the additional advantage that they can be used for the sensing of small molecules.…”