The use of gold nanoparticles (AuNP) has been established in nanocarriers, diagnostics, and biosensors. Access to the targeted sites of these nanomaterials could directly involve the first line of defense, the innate immune system. Charges of nanomaterials play a critical role in a number of aspects such as stabilization, cellular uptake, modulation, and function of cells. Interactions and modulations of the charged nanomaterials against the innate immune system may occur even at very low concentration. To understand the effects of charges on monocyte behavior, in this study, the positively and negatively charged AuNP (AuNP+ve and AuNP-ve) of the similar size and shape on cytotoxicity, recognition, cellular behavior, and function were evaluated in vitro using U937 human monocyte cells as an innate immunity model. Both types of AuNP at various concentrations (0−5 nM) exhibited low toxicity. In addition, the cellular internalization of the AuNP+ve and AuNP-ve, as determined by TEM, occurred by different mechanisms, and the internalization had no effect on cellular destruction, as implied by the low levels of %LDH. Interestingly, the AuNP+ve recognition and internalization seemingly entered cells through receptor dependence and strongly affected cellular response to express both pro-inflammatory (IL-1β) and anti-inflammatory (TGF-β) cytokines, while the AuNP-ve stimulated TNF-α expression. Nevertheless, the AuNP-treated cells maintained normal function when exposed to planktonic bacteria. Thus, these results indicated that one part of the immune system interacted with different surface-charged AuNP, suggesting appropiate immunomodulation in biomedicine.

In this work, the covalently oriented conjugation of monoclonal Listeria monocytogenes antibody (mAb-Lis) to amino-terminated oligo(ethylene glycol)-capped gold nanoparticles (NH2-TEG-AuNPs) was studied. After NH2-TEG-AuNPs were synthesized, the amino-terminated ligands on the particles were then linked to the carboxyl groups in the mAb-Lis through EDC/NHS chemistry. By maintaining the pH of the solution at ∼5, the Fc region of the antibody could preferably attach to the particle surface, providing a specific Fab region that was available for binding with the target pathogen. The resulting mAb-NH-TEG-AuNPs could act as a colorimetric probe for L. monocytogenes based on a particular antigen–antibody interaction, which resulted in a drastic aggregation of particles. This caused the color of the colloidal solution to transition from red–pink to purple or even gray depending on the pathogen concentration. To perform quantitative analysis, the absorbance ratio of A 650/A 534 was monitored as a function of L. monocytogenes concentration using a spectrophotometer. The detection limit was very low at 11 CFU/mL. Furthermore, a lateral flow strip (LFS) was fabricated as a portable device for onsite utilization. LFS detection could be completed by the naked eye and by a smartphone. The detection limit of LFS was estimated to be 103 CFU/mL. Our methods exhibited a substantial improvement in sensitivity compared to that of previous studies on immuno-based nanoparticles. The assay could be completed in 15 min, and no cross reactivity by any pathogen was found. Hence, the designed AuNPs exhibit great promise for use in monitoring L. monocytogenes for food safety and in other applications.

Myristicafragrans Houtt. (Nutmeg) is a widely known folk medicine across several parts of Asia, particularly used in antimicrobial treatment. Bacterial resistance involves the expression of efflux pump systems (chromosomal norA and mepA) in methicillin-resistant Staphylococcus aureus (MRSA). Crude extract (CE) and essential oil (EO) obtained from nutmeg were applied as efflux pump inhibitors (EPIs), thereby enhancing the antimicrobial activity of the drugs they were used in. The major substances in CE and EO, which function as EPIs, in a descending order of % peak area include elemicin, myristicin, methoxyeugenol, myristicin, and asarone. Here, we investigated whether the low amount of CE and EO used as EPIs was sufficient to sensitize MRSA killing using the antibiotic ciprofloxacin, which acts as an efflux system. Interestingly, synergy between ciprofloxacin and CE or EO revealed the most significant viability of MRSA, depending on norA and mepA, the latter being responsible for EPI function of EO. Therefore, CE and EO obtained from nutmeg can act as EPIs in combination with substances that act as efflux systems, thereby ensuring that the MRSA strain is susceptible to antibiotic treatment.

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