Hf2li lock in amplifier

The current data were recorded with a combination of HF2LI Lock‐in Amplifier (Zurich Instruments) and DL1211 preamplifier at a sampling rate of 28.8 or 7.2 kHz. The raw data with high bandwidth (10 kHz) were then used to reduce the signal noise of the circuit by a low‐pass Butterworth filter at a frequency of 2 kHz. The additional filtered processes were carried out by MATLAB 2016b. QuB or a step finding algorithm was then used to idealize the filtered data based on the hidden Markov model.^[37, ^39] The dwell time of each signal event and the number of total events were extracted after the idealization. The extracted data were then analyzed with Origin 9.0. The dwell time was then fitted to a single‐exponential decay function and the average dwell time was generated. Data are presented as mean ± SD. For statistical test, One‐way ANOVA testing followed by a Tukey post‐hoc test was carried out across groups. Significance was defined as p ≤ 0.05. Statistical analysis was carried out using Origin 9.0.

The amplitude-modulation SKPM was operated combined with a Cypher S atomic force microscopy (AFM; Asylum Research, Oxford Instruments) and a HF2LI Lock-in amplifier (Zurich Instruments) in N₂-filled glovebox. The resonance frequency ω₀ and spring constant of AFM conducting tips are ~127 kHz and 5.0 Nm⁻¹, respectively.

The TPFE signal partially overlaps spectrally with the CARS signal. The majority of the TPFE can be collected using a spectral filter but the minor overlapping part presents a substantial background to the smaller CARS signal. To separate the contribution of the TPFE from the CARS signal, homodyne detection is used, in which the Stokes beam in the CARS process is modulated (on/off). As a result, the CARS signal, which depends on the presence of the Stokes, is modulated as well whereas the TPFE that is generated predominantly by the pump beam remains constant. By detecting only the modulated part of the signal around the CARS wavelength, we separate the CARS portion. We separately verified that the Stokes beam alone does not generate any significant TPFE. The Stokes beam is modulated by an acoustic optical modulator, with a square wave at 1 MHz generated by an SFG-2110 function generator (GW Instek, Taiwan). The resulting signal from the PMT is demodulated on a HF2LI Lock-in amplifier (Zurich Instruments, Switzerland). A low-pass filter at roughly the same frequency as the pixel sampling frequency is applied, to average the demodulated signal over a single pixel.

The PNPase-modified SiNW FET device was covered by a polydimethylsiloxane cube, which contained a hole of about 2 mm in diameter as a reaction chamber^{17 ,29} . The RNA substrates were kept warm at 65 °C and then quickly cooled to avoid the effect of the changeable structure. Then, a 60-μL RNA analog solution with a specific concentration was subsequently injected into the microchamber. The chamber temperature was precisely controlled with an INSTEC hot/cold chuck, which involved a proportion–integration–differentiation control system (±0.001 °C) and a liquid nitrogen cooling system. Using an HF2LI Lock-in Amplifier (Zurich Instruments), the source–drain voltage was kept at DC 0.3 V throughout all real-time electrical measurements. The current between the source electrode and the drain electrode was amplified through a DLL1211 preamplifier operating at 10⁷ V•A⁻¹ gain and recorded using the HF2LI Lock-in Amplifier equipped with a 5-kHz bandwidth low-pass filter at 28.8 or 7.2 kHz sampling rates.