An isothermal graphene oxide （GO）-based SYBR Green I fluorescence platform for sensitive detection of RNA transcription levels is proposed. Briefly, a synthesized T7 DNA template was transcribed by T7 RNA polymerase, to produce many copies of single-stranded （ss） RNA transcripts. The ssRNA transcripts were then hybridized with a label-free ssDNA probe which alone will be adsorbed on the GO surface. The resultant double-stranded （ds） RNA：DNA hybrids were incubated with GO and SYBR Green 1. Then the hybrid binding with SYBR Green I emits enhanced fluorescence for detection. Experimental results show that the detection limit of the method is 0.5 pmol]L of T7 DNA template. A calibration curve with a linearity range of 0.5 pmol[L to 5 nmol/L is established, thus, making quantitative analysis feasible. The method may become a powerful tool for RNA transcription detection due to its sensitivity, rapidity and convenience.
The generation of high-energy dual-wavelength domain wall pulse with a low repetition rate is demonstrated in a highly nonlinear fiber （HNLF）-based fiber ring laser. By introducing the intracavity birefringence-induced spectral filtering effect, the dual-wavelength lasing operation can be achieved. In order to enhance the cross coupling effect between the two lasing beams for domain wall pulse formation, a 215-m HNLF is incorporated into the laser cavity. Experimentally, it is found that the dual-wavelength domain wall pulse with a repetition rate of 77.67 kHz could be efficiently obtained through simply rotating the polarization controller （PC）. At a maximum pump power of 322 mW, the 655-nJ single pulse energy in cavity is obtained. The proposed configuration provides a simpler and more efficient way to generate high energy pulse with a low repetition rate.
