A rapid and sensitive colorimetric sensor for hypochlorite detection based on polyvinylpyrrolidone-stabilized gold nanoparticles.

It is important to develop simple and effective approaches for hypochlorite (OCl-) detection at trace levels due to its widespread use as a disinfectant especially for water treatments including drinking water. In this work, a simple, facile colorimetric sensor for the sensitive determination of hypochlorite was developed based on the oxidation of cysteine by OCl-, a process that prohibits the cysteine-triggered aggregation of Au nanoparticles (AuNPs) stabilized by polyvinylpyrrolidone. With this strategy, the concentration of OCl- could be detected with the naked eye and/or ultraviolet-visible spectroscopy, and the limit of detection for OCl- was 1.0 µM and 250 nM, respectively. Additionally, the proposed method shows excellent anti-interference capability against many other interfering ions and real water sample applicability.

Study of 256 fiber array biaxial LiDAR optical assembly measurements.

This paper presents a method for measuring the optical assembly results based on multi-beam biaxial LiDAR. This method analyzes the optical assembly parameters of a LiDAR system affecting the LiDAR operation, and an experimental measurement system is built using a collimator to simulate the infinity imaging field. An InGaAs infrared camera is used to take pictures of the laser spot from the LiDAR transmitter and receiver, and then fit the laser spot images with Gaussian equations to calculate the biaxial LiDAR optical assembly results. Finally, the possible effecting factors of LiDAR alignment results are analyzed. This method is experimentally proven to achieve the measurement of the optical assembly results of a large scale multi-beam LiDAR. The possibility of further optimizing the measurement method by shaping the transmit laser is also reported.

Study of SO2 measurement based on a dual optical path Fabry-Perot correlation spectroscopy.

This paper investigates a method for measuring SO2 concentration using Fabry-Perot interferometer correlation spectroscopy. In this method, the experimental system is designed as a separated beam, with the beam entering the F-P cavity at two incidence angles simultaneously to match the peak and valley positions of the SO2 absorption cross-section. The system achieves a 2σ detection limit of 28.2 ppm·m(15 cm) at a sampling frequency of 10 Hz. An outfield comparison experiment with the differential optical absorption spectroscopy method shows good agreement for the simultaneous measurement of SO2 concentration from sulfur combustion, with a correlation coefficient of R2 = 0.93. This study introduces a non-dispersive, highly accurate, and fast gas detection technique.

Sea-urchin-like Fe3O4@C@Ag particles: an efficient SERS substrate for detection of organic pollutants.

Ag-coated sea-urchin-like Fe3O4@C core-shell particles can be synthesized by a facile one-step solvothermal method, followed by deposition of high-density Ag nanoparticles onto the carbon surface through an in situ growth process, respectively. The as-synthesized Ag-coated Fe3O4@C particles can be used as a surface-enhanced Raman scattering (SERS) substrate holding reproducible properties under an external magnetic force. The magnetic function of the particles allows concentrating the composite particles into small spatial regions, which can be exploited to decrease the amount of material per analysis while improving its SERS detection limit. In contrast to the traditional SERS substrates, the present Fe3O4@C@Ag particles hold the advantages of enrichment of organic pollutants for improving SERS detection limit and recycled utilization.

Sensitive and selective SERS probe for trivalent chromium detection using citrate attached gold nanoparticles.

In this article, we have demonstrated a sensitive and selective surface enhanced Raman spectroscopy (SERS) probe, based on citrate-capped gold nanoparticles (AuNPs), for trivalent chromium (Cr(3+)) detection. After introducing Tween 20 to a solution of citrate-capped AuNPs, the as-prepared Tween 20/citrate-AuNP probe could recognize Cr(3+) at a 50 × 10(-9) M level in an aqueous medium at a pH of 6.0. Tween 20 can stabilize the citrate-capped AuNPs against conditions of high ionic strength. Due to the chelation between Cr(3+) and citrate ions, AuNPs undergo aggregation. As a result, it formed several hot spots and provided a significant enhancement of the Raman signal intensity through electromagnetic (EM) field enhancements. A detailed mechanism for tremendous SERS intensity change had been discussed. The selectivity of this system toward Cr(3+) was 400-fold, remarkably greater than other metal ions.

In situ photoreduced silver nanoparticles on cysteine: an insight into the origin of chirality.

A delicate system, that is, in situ photoreduced silver metal nanoparticles (NPs) formed from a combination of Ag(+) complexes with L- or D-cysteine, enables the introduction of chirality. This chirality is essentially programmed by a synergetic interplay between the CO(2)(-) and NH(3)(+) groups on cysteine, rather than the formation of a chiral metal core (see figure).