Amino-Functionalized Nitrogen-Doped Graphene-Quantum-Dot-Based Nanomaterials with Nitrogen and Amino-Functionalized Group Content Dependence for Highly Efficient Two-Photon Bioimaging

Abstract

We fabricated nanomaterials comprising amino-functionalized and nitrogen-doped graphene quantum dots (amino-N-GQDs) and investigated their photostability and intrinsic luminescence in the near-infrared spectrum to determine their suitability as contrast agents in two-photon imaging (TPI). We observed that amino-N-GQDs with a higher amount of bonded nitrogen and amino-functionalized groups (6.2%) exhibited superior two-photon properties to those with a lower amount of such nitrogen and groups (4.9%). These materials were conjugated with polymers containing sulfur (polystyrene sulfonate, PSS) and nitrogen atoms (polyethylenimine, PEI), forming amino-N-GQD–PSS–PEI specimens (amino-N-GQD-polymers). The polymers exhibited a high quantum yield, remarkable stability, and notable two-photon properties and generated no reactive oxygen species, rendering them excellent two-photon contrast agents for bioimaging. An antiepidermal growth factor receptor (AbEGFR) was used for labeling to increase specificity. Two-photon imaging (TPI) of amino-N-GQD (6.2%)-polymer-AbEGFR-treated A431 cancer cells revealed remarkable brightness, intensity, and signal-to-noise ratios for each observation at a two-photon excitation power of 16.9 nJ pixel−1 under 30 scans and a three-dimensional (3D) depth of 105 µm, indicating that amino-N-GQD (6.2%)-polymer-AbEGFR-treated cells can achieve two-photon luminescence with 71 times less power required for two-photon autofluorescence (1322.8 nJ pixel−1 with 500 scans) of similar intensity. This economy can minimize photodamage to cells, rendering amino-N-GQD-polymers suitable for noninvasive 3D bioimaging.

Promising Graphene-Based Nanomaterials and Their Biomedical Applications and Potential Risks: A Comprehensive Review

“…Several pieces of GQD research implicated the bioimaging and biosensor applications also can be based on two-photon fluorescence. Kuo et al prepared namino-N-GQDs characterized by high quantum production, excellent stability, and excellent two-photon imaging performances . High specificity was achieved through labeling with an antiepidermal growth factor receptor.…”

“…Kuo et al prepared namino-N-GQDs characterized by high quantum production, excellent stability, and excellent two-photon imaging performances. 69 High specificity was achieved through labeling with an antiepidermal growth factor receptor. Amino-N-GQD can scan A431 cancer cells with a depth of 105 μm.…”

A review on the cytotoxicity of graphene quantum dots: from experiment to simulation

“…[7][8][9] GQDs have achieved rapid growth as breakthrough tools for multiple purposes in various elds of science including photonics, composites, energy, 10,11 and electronics. 12 In particular, GQD-based nanomaterials have shown much promise in biomedical elds, particularly for diagnostics, 13,14 drug delivery, 15,16 and bioimaging 17,18 in vitro and in vivo. At the same time, questions about the biosafety of GQDs have also attracted much attention in recent years.…”

Facile Synthesis of Surface-Modified Carbon Quantum Dots (CQDs) for Biosensing and Bioimaging

“…The most advanced biosensing and bioimaging methods rely on the nanotechnology solutions [ 1 , 2 , 3 ]. Nanomaterials are widely applied for detecting assays production with active optical elements.…”