Layered hydrogen-bonded nucleotide-functionalized CdS nanoparticles for photoelectrochemical applications

Nitric oxide assisted C60 secondary ion mass spectrometry for molecular depth profiling of polyelectrolyte multilayers

RATIONALE

Secondary ion mass spectrometry (SIMS) with polyatomic primary ions provides a successful tool for molecular depth profiling of polymer systems, relevant in many technological applications. Widespread C60 sources, however, cause in some polymers extensive damage with loss of molecular information along depth. We study a method, based on the use of a radical scavenger, for inhibiting ion-beam-induced reactions causing sample damage.

METHODS

Layered polystyrene sulfonate and polyacrylic acid based polyelectrolyte films, behaving differently towards C60 beam-induced damage, were selected and prepared as model systems. They were depth profiled by means of time-of-flight (TOF)-SIMS in dual beam mode, using fullerene ions for sputtering. Nitric oxide was introduced into the analysis chamber as a radical scavenger. The effect of sample cooling combined with NO-dosing on the quality of depth profiles was explored.

RESULTS

NO-dosing during C60-SIMS depth profiling of >1 micrometer-thick multilayered polyelectrolytes allows detection, along depth, of characteristic fragments from systems otherwise damaged by C60 bombardment, and increases sputtering yield by more than one order of magnitude. By contrast, NO has little influence on those layers that are well profiled with C60 alone. Such leveling effect, more pronounced at low temperature, leads to a dramatic improvement of profile quality, with a clear definition of interfaces.

CONCLUSIONS

NO-dosing provides a tool for extending the applicability, in SIMS depth profiling, of the widely spread fullerene ion sources. In view of the acceptable erosion rates on inorganics, obtainable with C60, the method could be of relevance also in connection with the 3D-imaging of hybrid polymer/inorganic systems.

Calixarene assembly with enhanced photocurrents using P(SNS-NH2)/CdS nanoparticle structure modified Au electrode systems

Two novel calix[n]arene-adorned gold electrodes producing high photocurrent intensities were successfully constructed.

Quantum-dot-based photoelectrochemical sensors for chemical and biological detection

Quantum-dot-based photoelectrochemical sensors are powerful alternatives for the detection of chemicals and biochemical molecules compared to other sensor types, which is the primary reason as to why they have become a hot topic in nanotechnology-related analytical methods. These sensors basically consist of QDs immobilized by a linking molecule (linker) to an electrode, so that upon their illumination, a photocurrent is generated which depends on the type and concentration of the respective analyte in the immediate environment of the electrode. The present review provides an overview of recent developments in the fabrication methods and sensing concepts concerning direct and indirect interactions of the analyte with quantum dot modified electrodes. Furthermore, it describes in detail the broad range of different sensing applications of such quantum-dot-based photoelectrochemical sensors for inorganic and organic (small and macro-) molecules that have arisen in recent years. Finally, a number of aspects concerning current challenges on the way to achieving real-life applications of QD-based photochemical sensing are addressed.

Layer-by-layer self-assembly under high gravity field

In the present article, we have developed a facile and rapid method to fabricate a polyelectrolyte multilayer under high gravity field and investigated the difference of mass transfer in the diffusing process between LbL self-assembled technique under high gravity field (HG-LbL) and dipping assembly. Herein, we have employed polyethyleneimine and zinc oxide nanoparticles, which is a well-known UV blocking material with typical absorption properties in the range of 300-400 nm, as building blocks and applied hydrogen bonding as the driving force to construct the multilayer under HG-LbL and dipping assembly. The results show that, compared with dipping assembly, HG-LbL can highly improve the utilization and adsorption efficiency of building blocks by hastening the diffusing process, and meanwhile the resulting multilayer films still achieve comparable quality as those prepared from dipping assembly.

Facile method for the fabrication of robust polyelectrolyte multilayers by post-photo-cross-linking of azido groups

In this letter, we have developed a facile method to enhance the stability of polyelectrolyte multilayers. We fabricate conventional polyelectrolyte multilayers of PAH/PAA through electrostatic layer-by-layer (LbL) assembly and then postinfiltrate photosensitive cross-linking agent 4,4'-diazostilbene-2,2'-disulfonic acid disodium salt into the LbL films. After cross-linking by UV irradiation, the stability of the photo-cross-linked multilayer is highly improved as evidenced by the lack of dissolution under ultrasonication in saturated SDS aqueous solutions for 10 min. Moreover, by taking advantage of the different stability of the LbL film before and after UV irradiation, a patterned surface can be achieved.

Quartz crystal microbalance detection of DNA single-base mutation based on monobase-coded cadmium tellurium nanoprobe

A new method for the detection of point mutation in DNA based on the monobase-coded cadmium tellurium nanoprobes and the quartz crystal microbalance (QCM) technique was reported. A point mutation (single-base, adenine, thymine, cytosine, and guanine, namely, A, T, C and G, mutation in DNA strand, respectively) DNA QCM sensor was fabricated by immobilizing single-base mutation DNA modified magnetic beads onto the electrode surface with an external magnetic field near the electrode. The DNA-modified magnetic beads were obtained from the biotin-avidin affinity reaction of biotinylated DNA and streptavidin-functionalized core/shell Fe(3)O(4)/Au magnetic nanoparticles, followed by a DNA hybridization reaction. Single-base coded CdTe nanoprobes (A-CdTe, T-CdTe, C-CdTe and G-CdTe, respectively) were used as the detection probes. The mutation site in DNA was distinguished by detecting the decreases of the resonance frequency of the piezoelectric quartz crystal when the coded nanoprobe was added to the test system. This proposed detection strategy for point mutation in DNA is proved to be sensitive, simple, repeatable and low-cost, consequently, it has a great potential for single nucleotide polymorphism (SNP) detection.

Self-assembly of semiconductor quantum-dots on electrodes for photoelectrochemical biosensing

CdS nanoparticles linked through a duplex DNA to a Au electrode do not lead to a noticeable photocurrent upon their illumination in the presence of triethanolamine, TEOA, 20 mM, pH = 7.2. The intercalation of doxorubicin into the duplex DNA stimulates, however, the generation of a photocurrent. This is attributed to the trapping of photoexcited conduction-band electrons by the intercalator units that facilitates, by a hopping mechanism, the electron transport to the electrode. The oxidation of TEOA by valence band holes allows the formation of a steady state photocurrent. This basic phenomenon is used to probe the operation of a DNA-based machine through the assembly of CdS nanoparticles on a Au electrode. The machine includes a nucleic acid "track", (1), that binds a primer, (2), through hybridization to a predefined domain. In the presence of polymerase, the nucleotide mixture, dNTPs, and the nicking enzyme, the autonomous replication, nicking and displacement of the "waste product", (3), are activated. The "waste product" bridges the (5)-functionalized CdS nanoparticles and the nucleic acid (4)-functionalized Au electrode, resulting in the assembly of the nanoparticles on the electrode. The intercalation of doxorubicin into the DNA-CdS nanostructures results in the generation of photocurrents upon illumination in the presence of TEOA, pH = 7.2. The photocurrents are controlled by the time intervals used to operate the DNA machine.