Plasmon-enhanced nano-photosensitizers: game-changers in photodynamic therapy of cancers.

Plasmonic nanostructures can be used to tackle the shortcomings of conventional photosensitizers in photodynamic therapy (PDT) of cancers, including their low reactive oxygen species (ROS) quantum yield, stability, and targetability. However, the positive role of plasmonic nanostructures is not limited to their ability for ROS generation or singlet oxygen formation. The main advantage of plasmonic nanostructures relies on the collective oscillation of free electrons, the so-called surface plasmon resonance (SPR), which can trigger plenty of optical phenomena in their near-field. Surface plasmon resonance is highly dependent on the morphology, size, and composition of the plasmonic nanostructure, which can give one the ability to control the wavelength of light-matter interaction, which is highly desirable in PDT applications. This review has focused on the conjugation of plasmonic nanostructures with organic compounds, biological compounds, ceramic nanoparticles, polymeric nanoparticles, metal-organic frameworks (MOFs), and magnetic nanoparticles from a mechanistic point of view. Hybridization of plasmonic nanoparticles would enable plenty of optical mechanisms beneficial for the PDT process that has been extensively discussed by presenting the most recent efforts in each category. This review can be a useful guideline for researchers working on enhancing the efficiency of the PDT process and those interested in plasmon-enhanced phenomena by emphasizing the underlying mechanisms.

SPR-based assay kit for rapid determination of Pb2.

A recyclable optical nanosensor was developed by immobilizing l-tyrosine functionalized silver nanoparticles (AgNPs) on the polyethylene terephthalate (PET) substrate for rapid determination of Pb2+ ions. At first, the l-tyrosine functionalized AgNPs were assessed in the solution phase; the response time was lower than 15 s, and a limit of detection lower than 9 nM was obtained in the dynamic range of 1-1000 nM. For fabrication of the optical assay kit, the design of experiment (DOE) was used to optimize the immobilization efficiency of the nanoparticles on PET films by studying AgNO3 concentration and pH as two crucial parameters. The assay kit in optimal conditions showed a sharp localized surface plasmon resonance band suitable for sensitive determination of Pb2+. The fabricated sensor showed promising results for rapid determination of lead ions with the limit of detection value as low as 1 nM (S/N = 3). The sensor reproduced the obtained results even after three consecutive runs, which proved the recyclability of the optical assay kit. The recoveries of the spiked concentration in real samples were in the range of 95%-103%, which confirmed the applicability of the sensor in practical applications.

Simple SPR-based colorimetric sensor to differentiate Mg2+ and Ca2+ in aqueous solutions.

L-tryptophan functionalized AgNPs were successfully fabricated using a one-pot synthesis method and assessed as a colorimetric probe for rapid and accurate determination of Mg2+ ions. The developed sensor showed a selective response towards Mg2+ with no interference from Ca2+ in the wide concentration range of 1-200 µM. The sensor's response was optimized in the pH range of 9-10, which can be attributed to the protonation of amine groups and their interaction with Mg2+ ions. The stability and selectivity of the sensor were examined in different salt (NaCl) and other metal ions, respectively. The L-tryptophan-AgNPs sensor detected Mg2+ with the limit of detection of 3 µM, which is way lower than the concentration range of magnesium in human serum (0.75-1.05 mM). The recovery values of the developed sensor were in the range of 96-102% for the determination of Mg2+ in urine samples. The obtained performances proved the potential application of the developed sensor for clinical diagnostic of Mg2+ ions where an accurate and rapid response is needed.

Recent advances in functionalization of plasmonic nanostructures for optical sensing.

This review summarizes the progress that has been made in the use of nanostructured SPR-based chemical sensors and biosensors. Following an introduction into the field, a first large section covers principles of nanomaterial-based SPR sensing, mainly on methods using noble metal nanoparticles (spheres, cubes, triangular plates, etc.). The next section covers methods for functionalization of plasmonic nanostructures, with subsections on functionalization using (a) amino acids and proteins; (b) oligonucleotides, (c) organic polymers, and (d) organic compounds. Several tables are presented that give an overview on the wealth of methods and materials published. A concluding section summarizes the current status, addresses current challenges, and gives an outlook on potential future trends. This review is not intended to be a comprehensive compilation of the literature in the field but rather is a systematic overview of the state of the art in surface chemistry of plasmonic nanostructures. The ability of various ligands and receptors for functionalization of nanoparticles as well as their sensing capability is discussed.

Eco-friendly pesticide based on peppermint oil nanoemulsion: preparation, physicochemical properties, and its aphicidal activity against cotton aphid.

Using organic insecticides including plant oils, it is possible to design a new perspective for the control of insect pests. In this research, nanoemulsion formulations of Mentha piperita, wild-type essential oil (EO) were prepared utilizing high-energy ultrasonication process. Physicochemical properties of nanoemulsions were precisely studied by measurement various parameters including pH, viscosity, conductivity, and zeta potential. Experimental design by the aid of response surface methodology (RSM) was used to highlight the physicochemical roles of EO percentage (1% to 5% (v/v)) and surfactant concentration (3% to 15% (v/v)) for achieving minimum droplet diameter with high physical stability. The nanoemulsion formulations were then characterized using dynamic light scattering, transmission electron microscopy, and optical clarity. Afterward, an appropriate model between the variable factors (EO percentage and surfactant concentration) and the response (hydrodynamic particle size) was statistically developed. Under the optimum conditions, nanoemulsion with hydrodynamic particle size less than 10 nm with high physical stability is obtainable. Bioassay experiments were carried out to elucidate the effects of nanoemulsion on the cotton aphid. Synthesized nanoemulsion formulations showed relatively high contact toxicity (average value of LC50 was about 3879.5 ± 16.2 µl a.i./L) against the pest. On the basis of the obtained results, prepared nanoemulsion using M. piperita is potentially applicable as organic insecticides against cotton aphid. Graphical abstract.

Facile and on-line colorimetric detection of Hg2+based on localized surface plasmon resonance (LSPR) of Ag nanotriangles.

A rapid and sensitive colorimetric detection method for the determination of Hg2+ has been successfully developed in this research. Citrate-functionalized silver nanotriangles (AgTrngs) were synthesized via one-pot sodium borohydride method with the edge-length range of 30 - 40 nm. The obtained AgTrngs were fully characterized using UV-Vis spectrophotometry, transmission electron microscopy (TEM), energy dispersed spectroscopy (EDS) and X-ray diffractometer. The efficiency of the developed sensor was optimum at pH= 8 due to interfering effect of H+ ions for Hg2+ under acidic conditions. The successful detection of mercury in aqueous solutions in the concentration range of 10 nmol L-1-50 µmol L-1 indicated the applicability of the developed sensor for effective monitoring and controlling the level of Hg2+ in industrial effluents. The ability of Hg2+ ion to interact with Ag and form the Hg-Ag alloy (amalgam) over the surface of AgTrngs resulted in an obvious color change from blue to violet. UV-Vis spectrophotometry showed that the sensor has the limit of detection (LOD) value of as low as 4 nmol L-1 which was below the safety level of Hg2+ions (10 nmol L-1) in drinking water. The proposed method can be used for on-line determination of Hg2+ in the complex aqueous solutions.

Modified Finke-Watzky mechanisms for the two-step nucleation and growth of silver nanoparticles.

In this work, a new modification was made on the Finke-Watzky mechanism for investigating the nucleation and growth steps in the synthesis of silver nanoparticles (AgNPs). UV-vis spectrophotometry and transmission electron microscopy evaluations proved that the former linear form of Finke-Watzky mechanism is not efficient for describing the nucleation and growth steps of AgNPs synthesis. In this manner, the Finke-Watzky mechanism was modified by considering a reversible pseudo first-order reaction for nucleation step. In addition, no assumptions were made in mathematical calculations related to the rate law which were previously adapted by the researchers in this field; i.e. [A]0 > [A] and k 2[A] ≫ k 1. These considerations led to the development of a kinetic model that is more closely related to what really occurs within the synthesis system. Kinetics data were obtained in a well-known synthesis process of AgNPs namely as sodium borohydride reduction. Furthermore, it was elucidated that polyvinylpyrrolidone (PVP) retards both the nucleation and growth steps resulting in the isotropic growth of seeds; this effect subtly provides a tunable synthesis process for achieving desired size of AgNPs. Moreover, Fourier-transform infrared spectroscopy revealed that the nitrogen atoms present in the PVP molecules are responsible for the interaction of PVP with AgNPs.

Colorimetric detection of ammonia using smartphones based on localized surface plasmon resonance of silver nanoparticles.

In this work, a rapid and straightforward method was developed for colorimetric determination of ammonia using smartphones. The mechanisms is based on the manipulation of the surface plasmon band of silver nanoparticles (AgNPs) via the formation of Ag (NH3)2+ complex. This complex decreases the amount of AgNPs in the solution and consequently, the color intensity of the colloidal system decreases. Not only the variation in color intensity of the solution can be tracked by a UV-vis spectrophotometer, but also a smartphone can be employed to monitor the color intensity variation by RGB analysis. Ammonia, in the concentration range of 10-1000mgL-1, was successfully measured spectrophotometrically (UV-vis spectrophotometer) and colorimetrically (RGB measurement) with the detection limit of 180 and 200mgL-1, respectively. Linear relationships were also developed for both methods. Also, the response time of the developed colorimetric sensor was around 20s. Both of the colorimetric and spectrophotometric methods showed a reliable performance for determination of ammonia in the real samples.

Colorimetric determination of Timolol concentration based on localized surface plasmon resonance of silver nanoparticles.

In this work, a rapid and simple colorimetric method based on the surface plasmon resonance of silver nanoparticles (AgNPs) was developed for the detection of the drug Timolol. The method used is based on the interaction of Timolol with the surface of the as-synthesized AgNPs, which promotes aggregation of the nanoparticles. This aggregation exploits the surface plasmon resonance through the electric dipole-dipole interaction and coupling among the agglomerated particles, hence bringing forth distinctive changes in the spectra as well as the color of colloidal silver. UV-vis spectrophotometery was used to monitor the changes of the localized surface plasmon resonance of AgNPs at wavelengths of 400 and 550 nm. The developed colorimetric sensor has a wide dynamic range of 1.0 × 10(-7) M-1.0 × 10(-3) M for detection of Timolol with a low detection limit of 1.2 × 10(-6) M. The proposed method was successfully applied for the determination of Timolol concentration in ophthalmic eye-drop solution with a response time lower than 40 s.