In Situ Assay of Proteins Incorporated with Unnatural Amino Acids in Single Living Cells by Differenced Resonance Light Scattering Correlation Spectroscopy

Investigation on the Effect of Fluorescence Quenching of Calf Thymus DNA by Piperine: Caspase Activation in the Human Breast Cancer Cell Line Studies

In this study, we determined the interaction of piperine and calf thymus DNA (ct DNA) in Tris-HCl buffer solution at pH = 6.8 and also evaluated the binding mechanism through the data of multi-spectroscopic techniques along with thermal melting and viscosity measurements. The outcomes of fluorescence quenching confirmed the occurrence of interactions between piperine and ctDNA and pointed out the role of piperine as the quencher. In addition, the KSV values were measured at three different temperatures of 298, 303, and 308 K to be 4.5 × 107 M-1, 5.65 × 107 M-1, and 9.36 × 107 M-1, respectively, which suggested the dominance of dynamic mechanism as the fluorescence quenching of piperine-ctDNA. The thermodynamic parameters revealed the predominance of hydrophobic forces in the interaction of ctDNA with piperine. According to the resonance light scattering data, the formation of a complex between piperine and ctDNA led to the creation of a larger particle. Ethidium bromide (EB) and acridine orange (AO) displacement studies, along with the ionic effects of NaCl and KI assessments, confirmed the interaction of piperine-ctDNA through a groove binding mode. The melting temperature assay of ctDNA upon the addition of piperine concentration indicated the probable groove binding of piperine to ctDNA, which was affirmed by relative viscosity measurement as well. The lack of detecting any alterations in the circular dichroism (CD) spectrum of CD investigation verified as a characteristic sign of groove binding mechanism and also confirmed all the experimental results with regard to the binding of piperine-ctDNA complex. Next to observing a concentration and time-dependent cytotoxicity in MDA-MB-231 cells, the impact of piperine on increasing lipid peroxidation and decreasing the activity of superoxide dismutase was also noticed. Apparently, piperine is capable of inducing caspase-3 activity as well.

Resonance Light-Scattering Correlation Spectroscopy and Its Application in Analytical Chemistry for Life Science

Resonance light-scattering correlation spectroscopy (RLSCS) is a new single-particle detection method with its working principle being like fluorescence correlation spectroscopy (FCS). RLSCS is obtained by autocorrelation function analysis on the measured fluctuation of the resonance light scattering (RLS) intensity occurring within a subfemtoliter volume when a single nanoparticle (such as gold nanoparticles (NPs) or silver (SNPs)) freely diffuses through the volume. The RLSCS technique can detect such parameters as concentration, diffusion coefficient (translation and rotation), etc. Compared with the FCS technique, the correlated fluorescence intensity signal in RLSCS is replaced with the RLS signal of the nanoparticles, overcoming some limits of the fluorescent probes such as photobleaching under high-intensity or long-term illumination. In this Account, we showcase RLSCS methods, theoretical models at different optical configurations, and some key applications. First, the RLSCS optical detection system was constructed based on the confocal optics, its theoretical model was proposed, and the diffusion behaviors of the nanoparticles in the solution were studied including the rotational and translational diffusion. And, methods were developed to measure the concentration, size, aspect ratio, and size distribution of the NPs. Second, based on the RLSCS methods, some detection strategies were developed for homogeneous DNA detection, immunoassay, apoptosis assay, self-thermophoresis of the nanomotor, and quantitative assay in single living cells. Meanwhile, a new fluorescence/scattering cross-correlation spectroscopy (FSCCS) method was proposed for monitoring the molecule-particle interaction. This method enriched the conventional fluorescence/fluorescence cross-correlation spectroscopy (FCCS) method. Third, using the EMCCD with high sensitivity and rapid response as an optical detector, two temporospatially resolved scattering correlation spectroscopy methods and their theoretical models were developed: total internal reflection (TIR) configuration-based spatially resolved scattering correlation spectroscopy (SRSCS) and dark-field illumination-based scattering correlation spectroscopy (DFSCS). These methods extended single-spot confocal RLSCS to imaging RLSCS, which makes RLSCS have the ability for multiple channel detection with temporospatial resolution. The method was successfully used for investigating the dynamic behaviors of gold NPs in live cells and obtained its temporospatial concentration distribution and diffusion behaviors. The final section of this Account outlines future directions in the development of RLSCS.

Probing the Protein Corona of Nanoparticles in a Fluid Flow by Single-Particle Differenced Resonance Light Scattering Correlation Spectroscopy

The protein corona of nanoparticles (NPs) plays a crucial role in determining NPs' biological fates. Here, a novel measurement strategy was proposed to in situ investigate the protein corona formed in the NPs with the home-built dual-wavelength laser-irradiated differenced resonance light scattering correlation spectroscopy (D-RLSCS) technique, combined with the modified generation method of the D-RLSCS curve. With the measurement strategy, the dissociation constants and the binding rates between proteins and gold nanoparticles (GNPs) were determined based on the binding-induced ratiometric diffusion change of NPs (the ratio of characteristic rotational diffusion time to translational one), using the formation of the protein corona of bovine serum albumin (BSA) or fibrinogen (FIB) on gold nanoparticles as a model. It was found that BSA shows a stronger binding constant and faster binding rate to gold nanospheres (GNSs) compared with those of FIB. Meanwhile, the dynamic behavior of the protein corona in a fluid flow mimicking biological vessels was further studied based on the combination of the D-RLSCS technique with a microfluidic channel. The measurement results indicated that some "loose" protein corona layers would strip off the surface of NPs within the microchannel due to the fluid sheath force. This method can provide the comprehensive information of a protein corona by averaging the diffusion behavior of many particles different from some conventional methods and overcome the shortcomings of conventional correlation spectroscopy methods.

Brightness Analysis per Moving Particle: In Situ Analysis of Alkaline Phosphatase in Living Cells

In situ quantitative analysis of enzymes such as phosphatase is important to understand a number of involved biological processes ranging from various metabolisms to signal transduction and cellular regulation. In this paper, a novel in situ measurement strategy was proposed to detect alkaline phosphatase (ALP) activity in different locations within single living cells. The principle is based on the measurement of the resonance light scattering brightness ratio (SBR) per moving nanoparticle that forms in an ALP-related chemical reaction. In the method, a novel resonance light scattering correlation spectroscopy (RLSCS) system was developed using two lasers for illumination or two detection channels. Using the gold nanoparticles (AuNPs) as probes, the Au@Ag nanoparticles (Au@Ag NPs) formed due to the ALP-catalyzed hydrolysis of ascorbic acid 2-phosphate (AAP) and the subsequent reduction-deposition reaction of Ag ions that occurred on the AuNPs. The SBR value per moving particle was determined based on the obtained RLS intensity traces and RLSCS curves. The SBR value was found to be not influenced by the intracellular viscosity and size that was confirmed in the experiments. The linear relation between the SBR and ALP activity was established and applied to detect ALP activity and evaluate the inhibition of different drugs. Finally, the method was successfully used to in situ measure ALP activity within living cells. The method overcomes the shortcoming of conventional methods that lack quantitative analysis and are susceptible to intracellular viscosity.

Photonic and Magnetic Dual-Responsive Molecularly Imprinted Sensor for Highly Specific Recognition of Enterovirus 71

The specific identification and detection of a virus are the critical factors to identify and control an epidemic situation. In this study, a novel photonic-magnetic responsive virus-molecularly imprinted photochemical sensor was constructed for recognition of enterovirus 71. As designed, the double-bond-modified magnetic metal organic framework and 4-(4'-acryloyloxyazo) benzoic acid were used as a magnetic carrier and light-responsive functional monomer, respectively. The structure of the recognition site of the virus-molecularly imprinted nanospheres can be photo-switched between two different structures to achieve rapid release and specific binding to the target virus. Additionally, the introduction of a magnetic core enables a rapid separation and recycling of imprinted particles. The device achieves a performance with high-specificity recognition (imprinting factor = 5.1) and an ultrahigh sensitivity with a detection limit of 9.5 × 10^-3 U/mL (3.9 fM). Moreover, it has good reproducibility and can be stored for as long as 6 months. Thus, the approach used in this work opens a new avenue for the construction of multiresponsive virus sensors.