Previously, PbS/CdS core/shell quantum dots with excellent optical properties have been widely used as light-harvesting materials in solar cell and biomarkers in bio-medicine. However, the nonlinear absorption characteristics of PbS/CdS core/shell quantum dots have been rarely investigated. In this work, PbS/CdS core/shell quantum dots were successfully employed as nonlinear saturable absorber (SA) for demonstrating a mode-locked Er-doped fiber laser. Based on a film-type SA, which was prepared by incorporating the quantum dots with the polyvinyl alcohol (PVA), mode-locked Er-doped operation with a pulse width of 54 ps and a maximum average output power of 2.71 mW at the repetition rate of 3.302 MHz was obtained. Our long-time stable results indicate that the CdS shell can effectively protect the PbS core from the effect of photo-oxidation and PbS/CdS core/shell quantum dots were efficient SA candidates for demonstrating pulse fiber lasers due to its tunable absorption peak and excellent saturable absorption properties.

Nucleos(t)ide analogue (NUC) resistance is an important clinical risk resulting from long-term therapy in chronic hepatitis B (CHB) management. Discontinuation of NUCs is a feasible strategy to reduce resistance. We aimed to observe the outcomes after NUC withdrawal in HBeAg-positive CHB patients. A total of 97 patients (11 patients with HBsAg loss and 86 patients with sustained HBeAg seroconversion) were enrolled. HBV DNA levels and alanine aminotransferase (ALT) levels were monitored regularly after discontinuation. Relapse was defined as HBV DNA levels >2000 IU/mL in at least two determinations more than 4 weeks apart. HBeAg seroconversion was achieved within 48 weeks (interquartile range (IQR), 24-72 weeks). The time on consolidation therapy was 96 weeks (IQR, 84-144 weeks). No relapses occurred for HBsAg loss patients. Evidence of relapse was observed in 9.3% of HBeAg seroconversion patients. All relapse cases occurred within 48 weeks after discontinuation. The time to relapse was 33 ± 15 weeks. Elevation of HBV DNA and ALT levels over baseline were only observed in 12.5% of relapse patients. There were no significant differences in baseline characteristics (sex, HBV genotype, age or ALT levels) or time on consolidation therapy between patients with relapse or sustained response. NUC discontinuation in HBeAg-positive CHB patients is feasible after achieving HBeAg seroconversion at a minimum of 24 weeks. There is further benefit to prolonging the time on consolidation therapy to reduce relapse. More than 48 weeks of sustained response is a predictive marker for long-term sustained response.

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