Powerful soft actuators that can perform programmable actuations are highly desired for the development of soft robotics. Herein, we report a moisture-driven polymer actuator, PPA, which is a composite of poly­(3,4-ethylenedioxythiophene)/polyvinyl alcohol/copolymer of acrylic acid and 2-acrylanmido-2-methylpropanesulfonic acid. PPA can not only generate powerful actuation with a contractile stress up to 13 MPa, but can also perform programmable helical motions. PPA films with internal stress along the radial directions were prepared by a simple solution-casting method. Driven by moisture, rectangular strips cut from the same PPA film but with different cutting angles (the oblique angle between the long axis of the PPA strip and the radial axis of the PPA film) can perform direct bending and left-handed or right-handed helical motions, demonstrating the generation of chirality from asymmetric internal stress. By modulating the distribution of internal stress in PPA strips, their moving direction and speed are readily prescribed. The powerful and programmable PPA strips can be used to make soft devices, such as moisture-responsive switches and transporters. Our strategy of generating and utilizing internal stress in responsive polymers represents a promising platform for fabricating smart soft actuators.

Surface-enhanced Raman spectroscopy (SERS) as a powerful qualitative analysis method has been widely applied in many fields. However, SERS for quantitative analysis still suffers from several challenges partially because of the absence of stable and credible analytical strategy. Here, we demonstrate that the optimal hotspots created from dynamic surfaced-enhanced Raman spectroscopy (D-SERS) can be used for quantitative SERS measurements. In situ small-angle X-ray scattering was carried out to in situ real-time monitor the formation of the optimal hotspots, where the optimal hotspots with the most efficient hotspots were generated during the monodisperse Au-sol evaporating process. Importantly, the natural evaporation of Au-sol avoids the nanoparticles instability of salt-induced, and formation of ordered three-dimensional hotspots allows SERS detection with excellent reproducibility. Considering SERS signal variability in the D-SERS process, 4-mercaptopyridine (4-mpy) acted as internal standard to validly correct and improve stability as well as reduce fluctuation of signals. The strongest SERS spectra at the optimal hotspots of D-SERS have been extracted to statistics analysis. By using the SERS signal of 4-mpy as a stable internal calibration standard, the relative SERS intensity of target molecules demonstrated a linear response versus the negative logarithm of concentrations at the point of strongest SERS signals, which illustrates the great potential for quantitative analysis. The public drugs 3,4-methylenedioxymethamphetamine and α-methyltryptamine hydrochloride obtained precise analysis with internal standard D-SERS strategy. As a consequence, one has reason to believe our approach is promising to challenge quantitative problems in conventional SERS analysis.