Table 3.

Effects of capping agents of nanoparticles and their possible uses in bioimaging.

Sr. No.	Nanoparticles (NPs)	Capping Agent	Effect of Capping Agent	Bioimaging Application	Reference
1.	CdS QDs	Dextrin	Reduced toxicity of innate cadmium sulfide (CdS)	Used as fluorescent agent in in vitro and in vivo studies where maximum fluorescence was observed in kidney, liver, and brain	[151]
2.	Au NPs & DTA	Polyamidoamine (PAMAM) dendrimer	Improved X-ray attenuation, stability, biocompatibility, and enhanced blood circulation time	CT Imaging	[152]
3.	Bimetallic Au-Ag NPs	Folic acid (FA)-modified PAMAM dendrimer	25% higher X-ray attenuation than Omnipaque. In in vitro better CT imaging of cancer cells overexpressing FA receptors showed 2.3 to 2.7-fold higher uptake than the cells possessing low level of FA expression.	In vitro CT imaging in cancer cells	[153]
4.	Ag NPs	Acetylated-PAMAM dendrimer	Extended blood circulation time led to prolonged enhancement	X-ray CT contrast agent	[154]
5.	Au NPs	Acetylated-PAMAM dendrimer	Improved biocompatibility, 1.6 times higher X-ray attenuation compared to Omnipaque, specific targeting through receptor-mediated endocytosis	In vivo CT imaging	[155]
6.	Au NPs	Thiolated PEG & pluronic triblock copolymer (PEO–PPO–PEO)	Improved colloidal and optical stability and biocompatibility	Used as scattering probes for dark-field imaging of cancer cells under both in vitro and in vivo conditions	[156]
7.	Gd2O3 & PMNPs	Diethylene glycol polymer & Liposomes	No in vitro cytotoxic effects, sensitive contrast agent	MRI contrast agent and marker for cell tracking	[157]
8.	IONPs	Dextran	Biocompatible, superior T2 relaxation rate and high relaxivities led to clear distinguished signal imaging intensity of specific organ, tumor, and whole-body	MRI contrast agents	[158]
9.	Au NPs	Poly di(carboxylatophenoxy)phosphazene	Biocompatible and biodegradable	Can be used as contrast agents for photoacoustic imaging	[159]
10.	INPs	PEG	Biocompatible, extended high contrast vascular imaging and stability, selectively accumulated in tumor	Vascular and tumor imaging by Micro-CT	[160]
11.	Iodine-131 labeled Au NPs	Polyethyleneimine (PEI)	Improved X-ray attenuation coefficient, colloidal stability, cytocompatibility, and radiochemical stability in vitro	Single-photon emission computed tomography/computed tomography (SPECT/CT) imaging and radionuclide therapy	[161]
12.	Bi2S3 NPs & QDs	PEG-phospholipid bilayer	Enhanced CT contrast and fluorescence imaging capability, longer circulation time (>4 h) than iobitridol, biocompatibility, and safety.	Used for combined CT/fluorescence imaging	[162]
13.	Radioactive iodide-124 labeled Au NPs	PEG	Non-toxic, high stability, and sensitivity in various pH, serum, and in vivo conditions	In vivo tumor imaging through combined positron emission tomography and cerenkov luminescent imaging (PET/CLI).	[163]
14.	CuS [c(RGDfK)]	PEG	High efficacy and minimal side effects	Promising platform for image guided ablation therapy	[164]
15.	Au NPs	Glycol-chitosan	Simplest nanocomposite did not require antibodies or complex surface modification	Photoacoustic contrast agent	[165]
16.	Silica NPs	PEG & doping with cyanine 5.5 (Cy5.5) & cyanine 7 (Cy7) dyes	High colloidal stability in water and in biological environment, with absorption and fluorescence emission in the NIR field	Used to achieve optical and photoacoustic imaging	[166]
17.	Au NPs	Poly(perylene diimide) (PPDI) & PEG	Greater photothermal effect and a stronger photoacoustic signal	Used as photoacoustic (PA) agents under in vivo imaging and therapeutic evaluation	[167]
18.	Plectin-SPION-Cy7 or SPION-Cy7	DSPE-PEG-NH2	Highly accumulated in tumor, MIAPaCa2 and XPA-1 carcinoma cells but not in normal pancreatic tissues, liver, and kidney	Optical imaging and MRI	[168]
19.	Curcumin-Ag NPs complex	Polyvinylpyrrolidone (PVP)	Enhanced water solubility and bioavailability in a biological system without effecting its therapeutic potential. Fluorescence efficiency in cancer cellular medium is ∼2.37 times higher	Used as fluorescent probe in CT imaging	[169]
20.	Au NPs doped with silver	Gelatin	Improved stability, quantum yield, and fluorescence lifetime. Remarkable biocompatibility	Promising approach for imaging in a challenging tissue as skin	[170]
21.	MoO3 mixed with optoelectrochemically active dye complex (Ru(II))	Chitosan (CS)	Biocompatible	Used in intracellular imaging	[171]
22.	Au NPs	Zinnia elegans plant extract	Highly biocompatible and do not use any targeted ligand	Used as imaging agent in NIR region	[172]
23.	Ag NPs	4-mercaptobenzoic acid-capped	Enhanced fluorescent brightness, improved photostability, and low cytotoxicity	Used for simultaneous cellular imaging and photodynamic therapy	[173]
24.	N-doped fluorescent Si NPs with an ultra-high quantum yield	EDTA-2Na	Water dispersibility, higher stability, and biocompatibility	Used in cellular imaging	[174]
25.	Carboxylated PPy-NPs	Folic acid functionalized carbon dots	Photostability, specific targeting, biocompatible	Used as PTT imaging agent	[175]

Gold nanoparticles (Au NPs); cadmium sulfide quantum dots (CdS QDs); radiodense iodine-containing compound (DTA); silver nanoparticles (Ag NPs); gadolinium oxide (Gd₂O₃); paramagnetic nanoparticles (PMNPs); iron oxide nanoparticles (IONPs); iodine nanoparticles (INPs); bismuth sulfide (Bi₂S₃); quantum dots (QDs); copper sulfide (CuS); polyethylene glycol (PEG); cyclic RGDfK peptide (cRGDfK); 1,2-Distearoyl-sn-glycero-3-phosphoethanolamine-N-amino(polyethylene glycol) (DSPE-PEG-NH2); superparamagnetic iron oxide (Fe₃O₄) nanoparticles (SPION) conjugated with plectin-1 antibody and Cy7 (Plectin-SPION-Cy7) (SPION-Cy7); Molybdenum trioxide (MoO₃), Ruthenium(II)-bipyridine complex (Ru(II)), Ethylenediaminetetraacetic acid disodium salt (EDTA-2Na), Polypyrrole nanoparticles (PPy-NPs).