Terahertz signature detection of biological samples in aqueous solution remains a great challenge due to the strong terahertz absorption of water. Here we propose a new preparation process for fabricating a microfluidic chip and use it as an effective sensor to probe the terahertz absorption signatures of microcystin aptamer (a linear single-stranded DNA with 60 nucleotides) dissolved in TE buffer with different concentrations. The microfluidic chip made of silicon includes thousands of 2.4 μm × 2.4 μm square-cross-section channels. One repeatable terahertz absorption signature is detected and recognized around 830 GHz, fitted to a Lorentz oscillator. This signature is theorized to originate from the bending of hydrogen bonds formed between adjacent hydrated DNA bases surrounded by water molecules. Furthermore, the low-lying vibrational modes are also investigated by molecular dynamics simulations which suggest that strong resonant oscillations are highly probable in the 815–830 GHz frequency band.

Dyes and heavy metals pollute the environment. Biochar-based hydrogel is an excellent adsorbent, but the competitive adsorption mechanism associated with the removal of pollutants using biochar is yet to be understood in detail. Biochar was prepared following the process of high-temperature lysis of marine green tide (Enteromorpha prolifera). The prepared biochar was cross-linked with water-soluble chitosan and compounded with nano-Fe₃O₄ to synthesize magnetically-modified Enteromorpha prolifera-based biochar hydrogel (MM-EBC-HD). The competitive removal performance of the hydrogel was studied, and the pollutant removal mechanism was analyzed against a binary system consisting of common environmental pollutants (methyl orange [MO] and hexavalent chromium [Cr (VI)]. The physical and chemical properties of the composites were studied before and after contaminant removal, and the associated pollutant removal mechanisms were analyzed by SEM, EDS, FTIR, XRD, and XPS techniques. The effects of pH, temperature and initial pollutant concentration on the adsorption performance of the materials were examined. The maximum adsorption of MO on MM-EBC-HD was 71.18 mg g⁻¹, and adsorption equilibrium was attained at approximately 60 min. Electrostatic forces, hydrophobic bonds, and hydrogen bonds were exploited for MO adsorption. And the maximum adsorption amount of Cr (VI) was recorded to be 115.41 mg g⁻¹, and equilibrium was attained in approximately 10 min. Electrostatic and ion exchange effects were exploited to adsorb Cr (VI) efficiently. The MO and Cr (VI) adsorption processes could be explained by the second-order kinetic model and Langmuir adsorption isotherms, respectively. The adsorption performance recorded for the binary adsorption system was poorer than that recorded for the single adsorption system for both pollutants. MO and Cr (VI) adsorption decreased from 74.88% to 47.65% and from 62.33% to 42.4%, respectively. Competition between MO and Cr (VI) in the dual system can be attributed to the presence of amino and hydroxyl groups. The MO–Cr complex, which was more compact in structure than a single contaminant, was formed, allowing few reactive groups to be exposed to the surface of the hydrogel. Additionally, MM-EBC-HD nanocomposites presented a recovery rate of 87% after 5 cycles and thus could be used to avoid adsorbents-caused environmental hazards. Graphical Abstract

The integration of a microfluidic chip into terahertz time-domain attenuated total reflection (THz TD-ATR) spectroscopy is highly demanded for the accurate measurement of aqueous samples. Hitherto, however little work has been reported on this regard. Here, we demonstrate a strategy of fabricating a polydimethylsiloxane microfluidic chip (M-chip) suitable for the measurement of aqueous samples, and investigate the effects of its configuration, particularly the cavity depth of the M-chip on THz spectra. By measuring pure water, we find that the Fresnel formulae of two-interface model should be applied to analyze the THz spectral data when the depth is smaller than 210 μm, but the Fresnel formula of one-interface model can be applied when the depth is no less than 210 μm. We further validate this by measuring physiological solution and protein solution. This work can help promote the application of THz TD-ATR spectroscopy in the study of aqueous biological samples.

Conformational changes of proteins play a vital role in implementing their functions and revealing the underlying mechanisms in various biological processes. It is still challenging to monitor protein conformations with temporal fingerprints of current–resistance pulses in the nanopore technique. Here the low-resolution morphologies of different conformations of a typical integrin, α_xβ₂, were estimated via relative blockade currents simulated from all-atom molecular dynamics (MD). Distinct conformational states of α_xβ₂ were directly explained by the volume and shape identifiers. Protein modulation in ionic current was analyzed from the conductivity distribution inside the protein-blocked nanopore. Combining a discrete model with spheroidal approximation, a MD-based approach was developed to theoretically predict the volume and shape of the nanopore for sensing α_xβ₂. This method was also applicable in specifying morphological identifiers of six other proteins, and the theoretical predictions are in good agreement with the experimental measurements. These results potentiated the validity of this method for the conformational identification of proteins in nanopores.