Following the Chemical Immobilization of Membrane Proteins on Plasmonic Nanoantennas Using Infrared Spectroscopy

A novel Affi-Cova magnetic nanoparticles for one-step covalent immobilization of His-tagged enzyme directly from crude cell lysate

Owing to the rapid advancement of in vitro synthetic biology, functional carriers capable of covalently binding target proteins from crude lysates under mild conditions have garnered escalating attention. Herein, a magnetic nanoparticle with affinity/covalent bifunction (MNP@Affi-Cova) was developed for the direct covalent immobilization of the recombinant enzyme of His-tagged birA (r-birA) from crude cell lysates in a single step. This innovative approach is attributed to the presence of chelated Ni2+ ions and epoxy groups on the surface of the beads. The fabricated magnetic nanoparticles were characterized by SEM, FT-IR spectrum, and zeta potential. The application conditions and stability of the MNP@Affi-Cova beads were systematically evaluated. Notably, the MNP@Affi-Cova beads exhibited a covalent capture efficiency of 91.25 μg r-birA/mg beads from a cell lysate supernatant containing 2.62 mg/mL crude protein. The immobilized r-birA exhibited significantly enhanced pH and thermal stability compared to the free counterpart. Additionally, the reusability of the immobilized r-birA on MNP@Affi-Cova demonstrated the retention of 76.1 % of its initial activity over ten cycles. These results suggest that the MNP@Affi-Cova presents considerable potential as a support for the covalent immobilization of recombinant His-tagged enzymes directly from crude lysates, thereby circumventing the labor-intensive purification process typically required before enzyme immobilization.

Towards multi-molecular surface-enhanced infrared absorption using metal plasmonics

Surface-enhanced infrared absorption (SEIRA) leads to a largely improved detection of polar molecules, compared to standard infrared absorption. The enhancement principle is based on localized surface plasmon resonances of the substrate, which match the frequency of molecular vibrations in the analyte of interest. Therefore, in practical terms, the SEIRA sensor needs to be tailored to each specific analyte. We review SEIRA sensors based on metal plasmonics for the detection of biomolecules such as DNA, proteins, and lipids. We further focus this review on chemical SEIRA sensors, with potential applications in quality control, as well as on the improvement in sensor geometry that led to the development of multiresonant SEIRA substrates as sensors for multiple analytes. Finally, we give an introduction into the integration of SEIRA sensors with surface-enhanced Raman scattering (SERS).

Moxa Wool in Different Purities and Different Growing Years Measured by Terahertz Spectroscopy

Moxa wool is a traditional Chinese herbal medicine, which can warm channels to dispel coldness. At present, there is no unified index to evaluate the purity and growing years of moxa wool in the market. Terpineol is one of the effective substances in the volatile oil of moxa wool. Here, we characterize the purity and growing years of moxa wool by studying terpineol. Gas chromatography-mass spectrometry (GC-MS) and high-performance liquid chromatography (HPLC) are the methods for monitoring terpineol at present, all of which have defects of complicated procedures. We established linear fitting to distinguish the different purities of moxa wool through the intensities (areas) of terpineol, the characteristic peaks, and the consequence presented; the coefficient of determination (R2) was higher than 0.90. Furthermore, based on the characteristic peak position of standard terpineol, the correlation model with the purity and growing year of moxa wool was set up, thereby differentiating the quality of moxa wool. We have built the partial least squares (PLS) model of the growing years of moxa wool with high accuracy, and the determination coefficient is greater than 0.98. In addition, we compare the quantitative accuracy of Raman spectroscopy with terahertz technology. Finally, a new method of terahertz spectroscopy to evaluate quality of moxa wool was found. It provides a new idea for the identification of inferior moxa wool in the market and a new method for identifying the quality of moxa wool in traditional Chinese medicine.

Plasmonic Resonant Nanoantennas Induce Changes in the Shape and the Intensity of Infrared Spectra of Phospholipids

Surface enhanced infrared absorption spectroscopic studies (SEIRAS) as a technique to study biological molecules in extremely low concentrations is greatly evolving. In order to use the technique for identification of the structure and interactions of such biological molecules, it is necessary to identify the effects of the plasmonic electric-field enhancement on the spectral signature. In this study the spectral properties of 1,2-Dipalmitoyl-sn-glycero-3 phosphothioethanol (DPPTE) phospholipid immobilized on gold nanoantennas, specifically designed to enhance the vibrational fingerprints of lipid molecules were studied. An AFM study demonstrates an organization of the DPPTE phospholipid in bilayers on the nanoantenna structure. The spectral data were compared to SEIRAS active gold surfaces based on nanoparticles, plain gold and plain substrate (Si) for different temperatures. The shape of the infrared signals, the peak positions and their relative intensities were found to be sensitive to the type of surface and the presence of an enhancement. The strongest shifts in position and intensity were seen for the nanoantennas, and a smaller effect was seen for the DPPTE immobilized on gold nanoparticles. This information is crucial for interpretation of data obtained for biological molecules measured on such structures, for future application in nanodevices for biologically or medically relevant samples.

Study of Membrane Protein Monolayers Using Surface-Enhanced Infrared Absorption Spectroscopy (SEIRAS): Critical Dependence of Nanostructured Gold Surface Morphology

Surface-enhanced infrared absorption spectroscopy (SEIRAS) is a powerful tool that allows studying the reactivity of protein monolayers at very low concentrations and independent from the protein size. In this study, we probe the surface's morphology of electroless gold deposition for optimum enhancement using two different types of immobilization adapted to two proteins. Independently from the mode of measurement (i.e., transmission or reflection) or type of protein immobilization (i.e., through electrostatic interactions or nickel-HisTag), the enhancement and reproducibility of protein signals in the infrared spectra critically depended on the gold nanostructured surface morphology deposited on silicon. Just a few seconds deviation from the optimum time in the nanoparticle deposition led to a significantly weaker enhancement. Scanning electron microscopy and atomic force microscopy measurements revealed the evolution of the nanostructured surface when comparing different deposition times. The optimal deposition time led to isolated gold nanostructures on the silicon crystal. Importantly, in the case of the immobilization using nickel-HisTag, the surface morphology is rearranged upon immobilization of linker and the protein. A complex three-dimensional (3D) network of nanoparticles decorated with the protein could be observed leading to the optimal enhancement. The electroless deposition of gold is a simple technique, which can be adapted to flow cells and used in analytical approaches.