Carbon dots stabilized silver-lipid nano hybrids for sensitive label free DNA detection.

Carbon dots have been extensively used for the development of fluorescent based molecular affinity sensors. However, label free DNA sensing by electrochemical method is not reported so far. Herein, we report carbon dots stabilized silver nanoparticles (CD-AgNPs) lipid nano hybrids as a sensitive and selective platform for label free electrochemical DNA sensing. The CD-AgNPs were synthesized by wet chemical method and then characterized by UV-visible, Fourier-transform Infra-red (FT-IR), dynamic light scattering (DLS) and high resolution transmission electron microscopy (HR-TEM) techniques. These CD-AgNPs were used for decorating the binary lipid 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) and N-[1-(2,3-Dioleoyloxy)propyl]-N,N,N-trimethylammonium chloride (DOTAP) surface (named as lipid) and tethered on self-assembled monolayer of 3-mercaptopropionic acid (MPA) (MPA-lipid-CD-AgNPs). The formation of array of MPA-lipid-CD-AgNPs on Au electrode was confirmed by atomic force microscopy (AFM). Electrochemical behavior of MPA- lipid-CD-AgNPs was monitored in the presence of 1 mM potassium ferri/ferrocyanide (K3/K4 [Fe(CN)6]). The formation of layer-by-layer MPA-lipid-CD-AgNPs is indicated by increased anodic and cathodic peak (ΔEp) separation with decreased redox peak current of K3/K4 [Fe(CN)6]. Short chain DNA (30 mer oligonucleotide, representing the lung cancer) was used as a model system for label free DNA sensing. Un-hybridized (single stranded DNA), hybridized (complementary hybridized), single, double and triple base mismatched target DNA hybridized surfaces were efficiently discriminated at 1 µM target DNA concentration at the Au/MPA-lipid-CD-AgNPs electrode by change in the charge transfer resistance from impedance technique. Further, the modified electrode was successfully used to determine target DNA in a wide linear range from 10-16 to 10-11 M. The present work open doors for the utilization of CDs in molecular affinity based electrochemical sensor design and development.

Fabrication of nitrogen-doped carbon dots for screening the purine metabolic disorder in human fluids.

Fabrication of nitrogen-doped carbon dots (N-CDs) electrode for the screening of purine metabolic disorder was described in this paper. Peroxynitrite is a short-lived oxidant species that is a potent inducer of cell death. Uric acid (UA) can scavenge the peroxynitrite to avoid the formation of nitrotyrosine, which is formed from the reaction between peroxynitrite and tyrosine (Try). Scavenging the peroxynitrite avoids the inactivation of cellular enzymes and modification of the cytoskeleton. Reduced level of UA decreases the ability of the body from preventing the peroxynitrite toxicity. On the other hand, the abnormal level of UA leads to gout and hyperuricemia. Allopurinol (AP) is administered in UA lowering therapy. Thus, the simultaneous determination of UA, Try and AP using N-CDs modified glassy carbon (GC) electrode was demonstrated for the first time. Initially, N-CDs were prepared from L-asparagine by pyrolysis and characterized by different spectroscopic and microscopic techniques. The HR-TEM image shows that the average size of the prepared N-CDs was 1.8±0.03nm. Further, the N-CDs were directly attached on GC electrode by simple immersion, follows Micheal's nucleophilic addition. XPS of N-CDs shows a peak at 285.3eV corresponds to the formation of C-N bond. The GC/N-CDs electrode shows higher electrocatalytic activity towards UA, Tyr and AP by not only shifting their oxidation potentials toward less positive potential but also enhanced their oxidation currents in contrast to bare GC electrode. The GC/N-CDs electrode shows the limit of detection of 13×10-10M (S/N=3) and the sensitivity of 924µAmM-1cm-2 towards the determination of UA. Finally, the N-CDs modified electrode was utilized for the determination of UA, Tyr and AP in human blood serum and urine samples.