Optical tweezers across scales in cell biology

Real-time monitoring of intracellular biochemical response in locally stretched single cell by a nanosensor

Mechanotransduction is the essential process that cells convert mechanical force into biochemical responses, and electrochemical sensor stands out from existing techniques by providing quantitative and real-time information about the biochemical signals during cellular mechanotransduction. However, the intracellular biochemical response evoked by mechanical force has been poorly monitored. In this paper, we report a method to apply local stretch on single cell and simultaneously monitor the ensuing intracellular biochemical signals. Specifically, a ferromagnetic micropipette was fabricated to locally stretch a single cell labeled with Fe3O4 nanoparticles under the external magnetic field, and the SiC@Pt nanowire electrode (SiC@Pt NWE) was inserted into the cell to monitor the intracellular hydrogen peroxide (H2O2) production induced by the local stretch. As a proof of concept, this work quantitatively investigated the elevated amount of H2O2 levels in single endothelial cell under different stretching amplitudes. This work puts forward a new research modality to manipulate and monitor the mechanotransduction at the single-cell level.

Enhanced forward scattering of a cell in line optical tweezers with an astigmatic beam

The line optical tweezers (LOT) has been proven to be an alternative technique to manipulating the biological cells because of the bigger potential compared with traditional optical tweezers with a highly focused spot. We deduce the 4 × 4 optical matrix of the astigmatic LOT to investigate the optical characteristics related to the systematic parameters. The comparison of the initial and scattered electric fields by the cell under the astigmatic and stigmatic LOT is implemented to illustrate that the forward scattered light from the astigmatic LOT is much stronger than that from the stigmatic LOT, so as to the cell deformations. It is demonstrated that the astigmatic LOT could provide a more efficient way to deform the cell not only in the focal plane, but also along the optical axis to screen large biomaterials in biomechanics.

Holographic Optical Tweezers That Use an Improved Gerchberg-Saxton Algorithm

It is very important for holographic optical tweezers (OTs) to develop high-quality phase holograms through calculation by using some computer algorithms, and one of the most commonly used algorithms is the Gerchberg-Saxton (GS) algorithm. An improved GS algorithm is proposed in the paper to further enhance the capacities of holographic OTs, which can improve the calculation efficiencies compared with the traditional GS algorithm. The basic principle of the improved GS algorithm is first introduced, and then theoretical and experimental results are presented. A holographic OT is built by using a spatial light modulator (SLM), and the desired phase that is calculated by the improved GS algorithm is loaded onto the SLM to obtain expected optical traps. For the same sum of squares due to error SSE and fitting coefficient η, the iterative number from using the improved GS algorithm is smaller than that from using traditional GS algorithm, and the iteration speed is faster about 27%. Multi-particle trapping is first achieved, and dynamic multiple-particle rotation is further demonstrated, in which multiple changing hologram images are obtained continuously through the improved GS algorithm. The manipulation speed is faster than that from using the traditional GS algorithm. The iterative speed can be further improved if the computer capacities are further optimized.

Analysis of Milk Microstructure Using Raman Hyperspectral Imaging

Optical spectroscopic analysis of the chemical composition of milk in its natural state is complicated by a complex colloidal structure, represented by differently sized fat and protein particles. The classical techniques of molecular spectroscopy in the visible, near-, and mid-infrared ranges carry only bulk chemical information about a sample, which usually undergoes a destructive preparation stage. The combination of Raman spectroscopy with confocal microscopy provides a unique opportunity to obtain a vibrational spectrum at any single point of the sample volume. In this study, scanning confocal Raman microscopy was applied for the first time to investigate the chemical microstructure of milk using samples of various compositions. The obtained hyperspectral images of selected planes in milk samples are represented by three-dimensional data arrays. Chemometric data analysis, in particular the method of multivariate curve resolution, has been used to extract the chemical information from complex partially overlaid spectral responses. The results obtained show the spatial distribution of the main chemical components, i.e., fat, protein, and lactose, in the milk samples under study using intuitive graphical maps. The proposed experimental and data analysis method can be used in an advanced chemical analysis of natural milk and products on its basis.