Malaria, caused by parasites of the species Plasmodium, is among the major life-threatening diseases to afflict humanity. The infectious cycle of Plasmodium is very complex involving distinct life stages and transitions characterized by cellular and molecular alterations. Therefore, novel single-cell technologies are warranted to extract details pertinent to Plasmodium-host cell interactions and underpinning biological transformations. Herein, we tested two emerging spectroscopic approaches: (a) Optical Photothermal Infrared spectroscopy and (b) Atomic Force Microscopy combined with infrared spectroscopy in contrast to (c) Fourier Transform InfraRed microspectroscopy, to investigate Plasmodium-infected erythrocytes. Chemical spatial distributions of selected bands and spectra captured using the three modalities for major macromolecules together with advantages and limitations of each method is presented here. These results indicate that O-PTIR and AFM-IR techniques can be explored for extracting sub-micron resolution molecular signatures within heterogeneous and dynamic samples such as Plasmodium-infected human RBCs.
Selective generation of an amine-terminated self-assembled monolayer bound to silicon wafers via a silicon-carbon linkage was realized by photocatalytically reducing the corresponding azide-terminated, self-assembled monolayers (Az-SAMs). The Az-SAM was obtained by thermal deposition of 11-chloroundecene onto a hydrogen-terminated silicon wafer followed by nucleophilic substitution of the chloride with the azide ion in warm N,N'-dimethylformamide (DMF). The presence of the terminal azide group on the SAM was confirmed by reflection absorption infrared spectroscopy (RAIRS), by X-ray photoelectron spectroscopy (XPS), and by detecting the formation of a triazole upon reaction of the azide with an activated alkyne. The desired terminal amine groups were generated by photocatalytic reduction of the Az-SAM with cadmium selenide quantum dots (CdSe Qdots) using λ > 400 nm. Analysis of the reduced SAM by XPS gave results that were consistent with those obtained with an amine-terminated surface obtained by reducing the Az-SAM with triphenylphosphine. To demonstrate the feasibility of using the Az-SAM for surface patterning, a sample was coated with adsorbed CdSe Qdots and exposed to the output of a diode laser at λ = 407 nm through a micropatterned mask. Using a SEM, the pattern formed in this manner was revealed after removing the CdSe Qdots and subsequently adsorbing 10 nm gold nanoparticles (AuNPs) to the positively charged terminal-amine groups. The formation of the pattern by CdSe-photocatalyzed reduction of the azide demonstrates a novel route to create features by selective modification of organic monolayers on silicon wafers.
The stability of Langmuir monolayers of CdSe Qdots capped with dodecan-ethiol (DDT), with dithiocarbamates having one, two, or three long alkyl chains (DTC-1, DTC-2 and DTC-3) or with tri-n-octylphosphine oxide (TOPO), was investigated and linked to the transport of Qdots into the subphase via a dissolution and diffusion mechanism. Langmuir films of Qdots were created by depositing droplets of purified Qdots in chloroform at the air-water interface. While holding the Qdot films at 13 mN/m for 1 h in a Langmuir trough, the average monolayer areas decreased by roughly 9% for TOPO-capped Qdots, â¼15-18% for the three DTC-capped Qdot preparations, and â¼21% for DDT-capped Qdots. Using the model of Ter Minassian-Saraga, the relative stabilities of the Qdot films studied were related to differences in equilibrium partitioning into the subphase and to apparent Qdot diffusivities within the subphase. An analysis of the Qdot preparations by Fourier-transform infrared spectroscopy (FTIR) revealed that the aliphatic tails of capping ligands were assembled on Qdot surfaces with similar packing densities for all ligand chemistries. A combined analysis of the film-area contraction and FTIR data suggested that, for the chemistries examined in this study, both the capping-ligand headgroup and the aliphatic tail groups impact Qdot Langmuir film stability through their joint influence on nanoparticle wettability and the tendency to aggregate upon partitioning into the subphase.
Polymer-inorganic nanocrystal composites offer an attractive means to combine the merits of organic and inorganic materials into novel electronic and photonic systems. However, many applications of these composites are limited by the solubility and distribution of the nanocrystals in the polymer matrices. Here we show that blending CdTe nanoparticles into a polymer-fullerene matrix followed by solvent annealing can achieve high photoconductive gain under low applied voltages. The surface capping ligand renders the nanoparticles highly soluble in the polymer blend, thereby enabling high CdTe loadings. An external quantum efficiency as high as approximately 8,000% at 350 nm was achieved at -4.5 V. Hole-dominant devices coupled with atomic force microscopy images show a higher concentration of nanoparticles near the cathode-polymer interface. The nanoparticles and trapped electrons assist hole injection into the polymer under reverse bias, contributing to efficiency values in excess of 100%.
Electric Conductivity , Fullerenes/chemistry , Nanoparticles/chemistry , Polymers/chemistry , Photochemistry/methods
Ordered, tightly packed aryl-azide-terminated, self-assembled monolayers (SAMs) were created on gold substrates from a new disulfide precursor. These monolayers were reduced at least partially in an aqueous environment using approximately 2 nm CdS quantum dots (Qdots) as photocatalysts to give mixed monolayers of arylamine- and aryl azide-terminated species. The CdS photocatalysts were made available for the reaction by exposure of the azide-terminated SAM to Qdots initially in solution or by preadsorption of the CdS nanoparticles on the SAM. In either case, X-ray photoelectron spectroscopy (XPS), grazing angle Fourier transform infrared spectroscopy (FTIR), and contact angle measurements were used to show the occurrence of the photocatalytic reduction. As further evidence for the presence of arylamine-terminated thiolate in the reduced SAM, these arylamine groups were successfully tagged with fluorescein isothiocyanate (FITC). The use of Qdot photocatalysts to functionalize surfaces may lead to a means to pattern surfaces at the nanoscale.
We have shown that CdS and CdSe nanoparticles can act as very efficient and highly chemoselective photocatalysts for the reduction of aromatic azides to aromatic amines. In several cases, the reaction proceeds with quantum yields near 0.5, which approaches the theoretical maximum for a two-electron process. The wide scope of the reaction was confirmed with compounds containing electron withdrawing (-NO(2), CO(2)R, COR) and electron donating groups (-OMe, -R, -Cl) at the para-, meta-, and ortho-positions. Remarkably, the reaction is relatively insensitive to the electron demands of the substituent. However, azides with meta-substituents give slightly lower yields than those with the same substituent at the ortho- or para-position.
