The Enhanced Photoluminescence Properties of Carbon Dots Derived from Glucose: The Effect of Natural Oxidation.

The investigation of the fluorescence mechanism of carbon dots (CDs) has attracted significant attention, particularly the role of the oxygen-containing groups. Dual-CDs exhibiting blue and green emissions are synthesized from glucose via a simple ultrasonic treatment, and the oxidation degree of the CDs is softly modified through a slow natural oxidation approach, which is in stark contrast to that aggressively altering CDs' surface configurations through chemical oxidation methods. It is interesting to find that the intensity of the blue fluorescence gradually increases, eventually becoming the dominant emission after prolonging the oxidation periods, with the quantum yield (QY) of the CDs being enhanced from ~0.61% to ~4.26%. Combining the microstructure characterizations, optical measurements, and ultrafiltration experiments, we hypothesize that the blue emission could be ascribed to the surface states induced by the C-O and C=O groups, while the green luminescence may originate from the deep energy levels associated with the O-C=O groups. The distinct emission states and energy distributions could result in the blue and the green luminescence exhibiting distinct excitation and emission behaviors. Our findings could provide new insights into the fluorescence mechanism of CDs.

Development of a highly sensitive ampicillin sensor utilizing functionalized aptamers.

To develop a sensitive and simple ampicillin (AMP) sensor for trace antibiotic residue detection, the influencing factors of the modification effect of nanogold-functionalized nucleic acid sequences (Adenine: A, Thymine: T) were comprehensively analyzed in this study, including the modification method, base length and type. It was found that under the same base concentration, longer chains are more likely to reach saturation than shorter chains; and when the base concentration and length are both the same, A exhibits a higher saturation modification level compared to T. Based on these research findings, a highly sensitive fluorescence aptamer sensor for detecting ampicillin was constructed using the optimized functionalized sequence (ployA6-aptamer) and experimental conditions (6 hours binding time between nucleic acid aptamer and complementary strand, pH 7 working solution, 20 minutes detection time) based on the principle of fluorescence resonance energy transfer. The sensor has a detection range of 0.18 ng ml-1 to 3.11 ng ml-1 for ampicillin, with a detection limit of 0.04 ng ml-1. It exhibits significant selectivity and achieves an average recovery rate of 98.71% in tap water and 91.83% in milk. This method can be used not only for residual ampicillin detection, but also for highly sensitive detection of various antibiotics and small biological molecules by replacing the aptamer type. It provides a research basis for the design of highly sensitive fluorescence aptamer sensors and further applications of nanogold@DNA composite structures.

Effect of the incident polarization on in-plane and out-of-plane spin splitting near the critical angle.

To reveal the effect of the incident polarization on the spin splitting of the photonic spin Hall effect (that is, the spatial and angular in-plane and out-of-plane spin splitting), we systematically study the phenomena and characteristics of these four spin splitting generated when the beam with arbitrary linear polarization is reflected from the non-absorbing medium interface and the absorbing medium interface. Several features of the relationship between the incident polarization and the four kinds of spin splitting are found. In addition, It is also found that the in-plane angular and spatial shifts are significantly enhanced near the critical angle, even reaching their theoretical upper limit. However, the out-of-plane shifts are not enhanced. The research in this paper will contribute to a deeper understanding of PSHE. These findings can also provide new ideas and methods for precision metrology, photonic manipulation, and photonic device fabrication.

Nanoscale film thickness measurement based on weak measurement.

In this paper, a novel method of film thickness measurement based on weak measurements is proposed by analyzing the quantitative relationship between film thickness and the weak measurement amplified shift of the photonic spin Hall effect, and the corresponding measurement system is established to verify it through experiments. This method can measure the thickness of an arbitrary dielectric film with nanometer resolution. The theoretical analysis and experimental results show that the method is reasonable, feasible, and reliable, and the structure of the measurement system is simple, easy to operate, and easy to assemble into a prototype instrument. The measurement model and method provide not only a new way for the measurement of thin film thickness but also an important reference for the precise measurement of other optical interface parameters.