Synthesis of High-Performance Photonic Crystal Film for SERS Applications via Drop-Coating Method

Antimicrobial Activities of Pistacia lentiscus Essential Oils Nanoencapsulated into Hydroxypropyl-beta-cyclodextrins

The rising risks of food microbial contamination and foodborne pathogens resistance have prompted an increasing interest in natural antimicrobials as promising alternatives to synthetic antimicrobials. Essential oils (EOs) obtained from natural sources have shown promising anticancer, antimicrobial, and antioxidant activities. EOs extracted from the resins of Pistacia lentiscus var. Chia are widely utilized for the treatment of skin inflammations, gastrointestinal disorders, respiratory infections, wound healing, and cancers. The therapeutic benefits of P. lentiscusessential oils (PO) are limited by their low solubility, poor bioavailability, and high volatility. Nanoencapsulation of PO can improve their physicochemical properties and consequently their therapeutic efficacy while overcoming their undesirable side effects. Hence, PO was extracted from the resins of P. lentiscusvia hydrodistillation. Then, PO was encapsulated into (2-hydroxypropyl)-beta-cyclodextrin (HPβCD) via freeze-drying. The obtained inclusion complexes (PO-ICs) appeared as round vesicles (22.62 to 63.19 nm) forming several agglomerations (180 to 350 nm), as detected by UHR-TEM, with remarkable entrapment efficiency (89.59 ± 1.47%) and a PDI of 0.1475 ± 0.0005. Furthermore, the encapsulation and stability of PO-ICs were confirmed via FE-SEM, 1H NMR, 2D HNMR (NOESY), FT-IR, UHR-TEM, and DSC. DSC revealed a higher thermal stability of the PO-ICs, reaching 351.0 °C. PO-ICs exerted substantial antibacterial activity against Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli as compared to free PO. PO-ICs showed significant enhancement in the antibacterial activity of the encapsulated PO against S. aureus with an MIC90 of 2.84 mg/mL and against P. aeruginosa with MIC90 of 3.62 mg/mL and MIC50 of 0.56 mg/mL. In addition, PO-ICs showed greater antimicrobial activity against E. coli by 6-fold with an MIC90 of 0.89 mg/mL, compared to free PO, which showed an MIC90 of 5.38 mg/mL. In conclusion, the encapsulation of PO into HPβCD enhanced its aqueous solubility, stability, and penetration ability, resulting in a significantly higher antibacterial activity.

Improved antimicrobial activities of Boswellia sacra essential oils nanoencapsulated into hydroxypropyl-beta-cyclodextrins

Natural antimicrobials have recently gained increasing interest over synthetic antimicrobials to overcome foodborne pathogens and food microbial contamination. Essential oils (EOs) obtained from Boswellia sacra resins (BO) were utilized for respiratory disorders, rheumatoid arthritis, malignant tumors, and viral infections. Like other EOs, the therapeutic potential of BO is hindered by its low solubility and bioavailability, poor stability, and high volatility. Several studies have shown excellent physicochemical properties and outstanding therapeutic capabilities of EOs encapsulated into various nanocarriers. This study extracted BO from B. sacra resins via hydrodistillation and encapsulated it into hydroxypropyl-beta-cyclodextrins (HPβCD) using the freeze-drying method. The developed inclusion complexes of BO (BO-ICs) had high encapsulation efficiency (96.79 ± 1.17%) and a polydispersity index of 0.1045 ± 0.0006. BO-ICs showed presumably spherical vesicles (38.5 to 59.9 nm) forming multiple agglomerations (136.9 to 336.8 nm), as determined by UHR-TEM. Also, the formation and stability of BO-ICs were investigated using DSC, FTIR, FE-SEM, UHR-TEM, 1H NMR, and 2D HNMR (NOESY). BO-ICs showed greater thermal stability (362.7 °C). Moreover, compared to free BO, a remarkable enhancement in the antimicrobial activities of BO-ICs was shown against three different bacteria: Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa. BO-ICs displayed significant antibacterial activity against Pseudomonas aeruginosa with an MIC90 of 3.93 mg mL-1 and an MIC50 of 0.57 mg mL-1. Also, BO-ICs showed an increase in BO activity against Escherichia coli with an MIC95 of 3.97 mg mL-1, compared to free BO, which failed to show an MIC95. Additionally, BO-ICs showed a more significant activity against Staphylococcus aureus with an MIC95 of 3.92 mg mL-1. BO encapsulation showed significantly improved antimicrobial activities owing to the better stability, bioavailability, and penetration ability imparted by encapsulation into HPβCD.

Coupling Au-loaded magnetic frameworks to photonic crystal for the improvement of photothermal heating effect in SERS

The combination of plasmonic metals and photonic crystal (PC) structure is considered to have potential for further enhancement of the surface-enhanced Raman scattering (SERS) effect in comparison with conventional metal SERS substrates. Many studies have suggested that SERS signals probably suffer from an often-neglected effect of strong surface plasmon resonance (SPR)-induced photothermal heating during SERS detection. Herein, we have discovered that the photothermal heating problem arises in a traditional hybrid substrate that is prepared by doping plasmonic Au nanoparticles (NPs) into the voids of an opal PC (Au-PC). This happens mainly because excess Au agglomerates formed by non-uniformly distributed Au NPs can cause a strong SPR effect under laser illumination. To fully address this issue, we have employed an improved hybrid substrate that is fabricated by substituting Au NPs in Au-PC with an Au-loaded magnetic framework (AuMF). The AuMF can effectively prevent the aggregation of Au NPs and ensure sufficient hot spots for SERS. This novel substrate prepared by doping AuMFs into a PC (AuMF-PC) was free of strong photothermal heating and showed high SERS intensity and reproducibility of the SERS signal compared with Au-PC. For practical applications, we have demonstrated AuMF-PC as an appropriate candidate for the SERS assay of the trace thiol pesticide thiram, and it enables recycling and reuse to achieve low cost.

A Robust Method for the Elaboration of SiO2-Based Colloidal Crystals as a Template for Inverse Opal Structures

Photonic crystals (PCs) are nanomaterials with photonic properties made up of periodically modulated dielectric materials that reflect light between a wavelength range located in the photonic band gap. Colloidal PCs (C-PC) have been proposed for several applications such as optical platforms for the formation of physical, chemical, and biological sensors based on a chromatic response to an external stimulus. In this work, a robust protocol for the elaboration of photonic crystals based on SiO₂ particle (SP) deposition using the vertical lifting method was studied. A wide range of lifting speeds and particle suspension concentrations were investigated by evaluating the C-PC reflectance spectrum. Thinner and higher reflectance peaks were obtained with a decrease in the lifting speed and an increase in the SP concentrations up to certain values. Seven batches of twelve C-PCs employing a SP 3% suspension and a lifting speed of 0.28 µm/s were prepared to test the reproducibility of this method. Every C-PC fabricated in this assay has a wavelength peak in a range of 10 nm and a peak width lower than 90 nm. Inverse-opal polymeric films with a highly porous and interconnected morphology were obtained using the developed C-PC as a template. Overall, these results showed that reproducible colloidal crystals could be elaborated on a large scale with a simple apparatus in a short period, providing a step forward in the scale-up of the fabrication of photonic colloidal crystal and IO structures as those employed for the elaboration of photonic polymeric sensors.