Transition Metal Ion (Mn2+, Fe2+, Co2+, and Ni2+)-Doped Carbon Dots Synthesized via Microwave-Assisted Pyrolysis: A Potential Nanoprobe for Magneto-fluorescent Dual-Modality Bioimaging

Sajid Abdul Rub Pakkath; Shashank Shankar Chetty; Praneetha Selvarasu; Arumugam Vadivel Murugan; Yogesh Kumar; Latha Periyasamy; Muthukamalam Santhakumar; Sudha Rani Sadras; Kirankumar Santhakumar

doi:10.1021/acsbiomaterials.7b00943

Transition Metal Ion (Mn²⁺, Fe²⁺, Co²⁺, and Ni²⁺)-Doped Carbon Dots Synthesized via Microwave-Assisted Pyrolysis: A Potential Nanoprobe for Magneto-fluorescent Dual-Modality Bioimaging

ACS Biomater Sci Eng. 2018 Jul 9;4(7):2582-2596. doi: 10.1021/acsbiomaterials.7b00943. Epub 2018 Jun 6.

Authors

Sajid Abdul Rub Pakkath, Shashank Shankar Chetty, Praneetha Selvarasu, Arumugam Vadivel Murugan, Yogesh Kumar, Latha Periyasamy, Muthukamalam Santhakumar, Sudha Rani Sadras, Kirankumar Santhakumar¹

Affiliation

¹ Zebrafish Genetics Laboratory, Department of Genetic Engineering, Sree Ramaswamy Memorial (SRM) Institute of Science and Technology, SRM Nagar, Kattankulathur, Tamil Nadu 603203, India.

PMID: 33435121
DOI: 10.1021/acsbiomaterials.7b00943

Abstract

Heteroatom-doped carbon dots (C-dots) have captured widespread research interest owing to high fluorescence and biocompatibility for multimodal bioimaging applications. Here, we exemplify a rapid, facile synthesis of ethylenediamine (EDA)-functionalized transition metal ion (Mn²⁺, Fe²⁺, Co²⁺, and Ni²⁺)-doped C-dots via one-pot microwave (MW)-assisted pyrolysis at 800 W within 6 min using Citrus limon (lemon) extract as a carbon source. During MW pyrolysis, the precursor extract undergoes simultaneous carbonization and doping of metal ions onto C-dot surfaces in the presence of EDA. The EDA-functionalized transition metal ion-doped C-dots (i.e., Mn/C, Fe/C, Co/C, and Ni/C-dots) are collectively termed as TMCDs. The water-soluble TMCDs exhibited a size of 3.2 ± 0.485 nm and were enriched with amino and oxo functionalities and corresponding metal-oxide traces on the surfaces, as revealed from Fourier transfer infrared and X-ray photoelectron spectroscopy analyses. Interestingly, TMCDs demonstrated excitation-wavelength-dependent emission with brighter photoluminescence (PL) at 460 nm. Compared to pristine C-dots with a PL quantum yield (QY) of 48.31% and a fluorescence lifetime of 3.6 ns, the synthesized Mn/C, Fe/C, Co/C, and Ni/C-dots exhibited PL QY values of 35.71, 41.72, 75.07, and 50.84% as well as enhanced fluorescence lifetimes (τ_av) of 9.4, 8.6, 9.2, and 8.9 ns, respectively. The TMCDs significantly exhibited enhanced biocompatibility in human colon cancer cells (SW480) for fluorescence bioimaging and showed ferromagnetic and superparamagnetic behavior with vibrant T₁-contrast ability. Interestingly, the maximum longitudinal (r₁) relaxivity of 0.341 mM^-1 s^-1 was observed for Mn/C-dots in comparison to that of 3.1-3.5 mM^-1 s^-1 of clinically used Gd-DTPA magnetic resonance (MR)-contrast agent in vitro (1.5 T). Similarly, the maximum longitudinal relaxivity (r₁) of 0.356 mM^-1 s^-1 was observed for Ni/C-dots (1.5 T) with respect to 4.16 ± 0.02 mM^-1 s^-1 attained for Gd-DTPA in vivo (8.45 T). Thus, the rapid, energy-efficient MW-assisted pyrolysis presents lemon extract derived, EDA-functionalized TMCDs with enhanced PL and efficient T₁ contrast as potential magneto-fluorescent nanoprobes for dual-modality bioimaging applications.

Keywords: T1-contrast nanoprobe; TMCD; fluorescence bioimaging; magnetic resonance imaging; microwave-assisted pyrolysis; natural extract; transition metal ion doped carbon dot.