Labeling of fibronectin by fluorescent and paramagnetic nanoprobes for exploring the extracellular matrix: bioconjugate synthesis optimization and biochemical characterization

Development of novel FRET aptasensor based on the quenching ability of iron oxide-gold nanostars for the detection of aflatoxin M1

Detecting Aflatoxin M1 (AFM1) in food products is crucial due to its high toxicity and health risks. This study introduced a fluorescence donor material using Rhodamine-B-Isothiocyanate (RBITC)-doped silica nanoparticles (RDSN) combined with iron oxide‑gold nanostars (IOGNS) as a quencher. The composite aptasensor (RDSN/IOGNS) served as a Förster Resonance Energy Transfer (FRET) nanoprobe for sensitive and selective AFM1 detection. The fluorescence of aptamer-conjugated RDSN (apt-RDSN) was effectively quenched by complementary DNA-conjugated IOGNS (cDNA-IOGNS). Upon AFM1 introduction, apt-RDSN dissociated from the IOGNS surface, restoring the fluorescence signal. The fluorescence intensity correlated linearly with AFM1 concentration, achieving a detection limit of 0.15 ng/mL. Compared to conventional enzyme-linked immunosorbent assay (ELISA), this FRET aptasensor showed excellent recovery rate and relative standard deviation (RSD) in milk samples, highlighting its potential for practical AFM1 detection applications.

Novel synthesis of fibronectin derived photoluminescent carbon dots for bioimaging applications

Fibronectin (FN) derived from human plasma has been used for the first time as the carbon precursor in the top-down, microwave-assisted hydrothermal synthesis of nitrogen doped carbon dots (CDs). FN is a large glycoprotein primarily known for its roles in cell adhesion and cell growth. Due to these properties FN can be over expressed in the extracellular matrix (ECM) of some cancers allowing FN to be used as an indicator for the detection of cancerous cells over non-cancerous cells. These FN derived CDs display violet photoluminescence with UV excitation and appear to possess similar functional groups on their surface to their carbon precursor (-COOH and -NH2). This is believed to be due to the self-passivation of the CDs' nitrogen-containing surface functional groups during the heating process. These CDs were then used to stain MCF-7 and MDA-231 breast cancer cells and were observed to interact primarily with the cell membrane rather than intercalating into the cell like the many other types of CDs. This led to the hypothesis that the CDs are selectively binding to the FN overexpressed within the cancer cells' ECM via amide linkages. This is in agreement with the EDX and FTIR spectra of the FN CDs which indicate the presence of -COOH and nitrogen containing surface groups like -NH3. The inherent selectivity of the CDs combined with their ability to photoluminesce enables their use as a fluorophore for bioimaging applications.

Modification of EDC method for increased labeling efficiency and characterization of low-content protein in gum acacia using asymmetrical flow field-flow fractionation coupled with multiple detectors

1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) is widely used as a crosslinker for fluorescence labeling of protein in the fields of biochemistry and food analysis. Many natural polysaccharides often contain some proteins or peptides that are very low in content but play a vital role in their biological function as well as technical applications. Determination of these low-content proteinaceous matters requires a highly sensitive and selective method. In this study, a methodological approach for investigations of the presence of proteinaceous material over the molar mass distribution (MD) of polysaccharides was developed using gum acacia (GA) as a model polysaccharide. EDC fluorescence-labeling method was modified by changing the pH (7, 9, and 11) of the solution for the analysis of low-content protein in food materials. Fluorescence spectroscopy and asymmetrical flow field-flow fractionation (AF4) were employed for characterizing the labeling efficiency and physiochemical properties of unlabeled and fluorescence-labeled GA. AF4 provided molar mass (M) and the radius of gyration (r_G) of arabinogalactan (AG) and arabinogalactan protein complex (AGP) and determined the presence of proteinaceous matter over the MD. The labeling efficiencies of GA at pH 7, 9, and 11 determined by fluorescence spectroscopy were 56.5, 68.4, and 72.0%, respectively, with an increment of 15.5% when pH was increased from 7 to 11. The modified EDC fluorescence-labeling method allows highly sensitive and selective analysis of low-content proteinaceous matters and their distribution in natural polysaccharides.

Asymmetric flow field-flow fractionation coupled to inductively coupled plasma mass spectrometry for the quantification of quantum dots bioconjugation efficiency

Hyphenation of asymmetric flow field-flow fractionation (AF4) to an on-line elemental detection (inductively coupled plasma-mass spectrometry, ICP-MS) is proposed as a powerful diagnostic tool for quantum dots bioconjugation studies. In particular, conjugation effectiveness between a "model" monoclonal IgG antibody (Ab) and CdSe/ZnS core-shell Quantum Dots (QDs), surface-coated with an amphiphilic polymer, has been monitored here by such hybrid AF4-ICP-MS technique. Experimental conditions have been optimized searching for a proper separation between the sought bioconjugates from the eventual free reagents excesses employed during the bioconjugation (QDs and antibodies). Composition and pH of the carrier have been found to be critical parameters to ensure an efficient separation while ensuring high species recovery from the AF4 channel. An ICP-MS equipped with a triple quadropole was selected as elemental detector to enable sensitive and reliable simultaneous quantification of the elemental constituents, including sulfur, of the nanoparticulated species and the antibody. The hyphenated technique used provided nanoparticle size-based separation, elemental detection, and composition analysis capabilities that turned out to be instrumental in order to investigate in depth the Ab-QDs bioconjugation process. Moreover, the analytical strategy here proposed allowed us not only to clearly identify the bioconjugation reaction products but also to quantify nanoparticle:antibodies bioconjugation efficiency. This is a key issue in future development of analytical and bioanalytical photoluminescent QDs applications.

Acridine orange coated magnetic nanoparticles for nucleus labeling and DNA adsorption

The magnetic-fluorescent nanoparticles are the integration of fluorophores and magnetic nanoparticles (MNP), which are superior to traditional single-modal nanoparticles. Here, we develop magnetic nanoparticles functionalized by acridine orange (ACO) for labeling nucleus and separating DNA. The ACO, a cell-permeant nucleic acid binding dye, is conjugated with amine on magnetic nanoparticles by glutaraldehyde-mediated coupling and characterized by TEM and FT-IR. Fluorescence spectroscopy, INCell analyzer, and confocal microscopy analyses confirmed the fluorescent property of ACO modified MNP. Furthermore, the modified magnetic nanoparticles showed strong intracellular fluorescence when incubated with 293T cells for a short period of time. The adsorption capacities measured at various concentrations showed enhanced adsorption capacities for double or single stranded DNA when compared to amine MNP conjugated with glutaraldehyde. The cell viability tests of the composite nanoparticles on 293T cells showed low cytotoxicity indicating the safeness of the nanoparticles. The modified magnetic nanoparticles pave a versatile platform for biological applications such as cell labeling and DNA adsorption.