Probing the structural evolution on the surface of cardiolipin vesicles with an amphiphilic second harmonic generation and fluorescence probe.

Investigating the influence of the ambient chemical environment on molecular behaviors in liposomes is crucial for understanding and manipulating cellular vitality as well as the capabilities of lipid drug carriers in various environments. Here, we designed and synthesized a second harmonic generation (SHG) and fluorescence probe molecule called Pyr-Py+-N+ (PPN), which possesses membrane-targeting capability. We employed PPN to investigate the response of lipid vesicles composed of cardiolipin to the presence of exogenous salt. The kinetic behaviors, including the adsorption and embedding of PPN on the surface of small unilamellar vesicles (SUVs) composed of cardiolipin, were analyzed. The response of the SUVs to the addition of NaCl was also monitored. A rapid decrease in vesicle size can be evidenced through the rapid drop in SHG emission originating from PPN located on the vesicle surface.

Temperature-Modulated Evolution of Surface Structures Induces Significant Enhancement of Two-Photon Fluorescent Emission from a Dye Molecule.

Fluorescence is an essential property of molecules and materials that plays a pivotal role across various areas such as lighting, sensing, imaging, and other applications. For instance, temperature-sensitive fluorescence emission is widely utilized for chemo-/biosensing but usually decreases the intensity upon the increase in temperature. In this study, we observed a temperature-induced enhancement of up to ∼150 times in two-photon fluorescence (TPF) emission from a dye molecule, 4-(4-diethylaminostyry)-1-methylpyridinium iodide (D289), as it interacted with binary complex vesicles composed of two commonly applied surfactants: sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB). By employing second harmonic generation (SHG) and TPF techniques, we clearly revealed the temperature-dependent kinetic behavior of D289 on the surface of the vesicles and utilized it to interpret the origin of the significant TPF enhancement. Additionally, we also demonstrated a similar heating-induced enhancement of the TPF emission from D289 on the membrane of phospholipid vesicles, indicating the potential application of TPF in temperature sensing in the biology systems. The embedding of D289 in the tightly packed alkane chains was identified as the key factor in enhancing the TPF emission from D289. This finding may provide valuable information for synthesizing fluorescence materials with a high optical yield.

Monitoring the response of a model protocell to dye and surfactant molecules through second harmonic generation and fluorescence imaging.

Probing the interaction between molecules and protocells is crucial for understanding the passive transport of functional molecules in and out of artificial and real cells. Second-harmonic generation (SHG) has been proven to be a powerful method for analyzing the adsorption and cross-membrane transport of molecules on lipid bilayers. In this study, we used SHG and two-photon fluorescence (TPF) imaging to study the interaction of charged dye molecules (D289) with a lipid vesicle. Unexpectedly, it was observed that the transport of D289 at a relatively high concentration is not as efficient as that at a lower dye concentration. Periodic shrinking of the model protocell and discharging of D289 out from the vesicle were revealed by combined analyses of SHG and TPF images. The response of the vesicle to a surfactant was also analyzed with D289 as a probe. This work demonstrates that the combined SHG and TPF imaging method is a unique approach that can provide detailed information on the interaction of molecules and lipids (both morphology and molecular kinetics). Determining these subtle interfacial kinetics in molecules is important for understanding the mechanism of many biophysical processes occurring on lipids.

Ultrafast synthesis of efficient TS-PtCoCu/CNTs composite with high feed-to-product conversion rate by Joule heating for electrocatalytic oxidation of ethanol.

Due to the challenges involved in achieving high metal load, uniform metal dispersion and nanosized metal particles simultaneously, it is difficult to develop a simple protocol for the rapid and efficient synthesis of Pt-based composites for electrocatalytic ethanol oxidation reaction (EOR). In this study, a facile ultrafast thermal shock strategy via Joule heating was applied to fabricate a series of PtCoCu ternary nanoalloys decorated carbon nanotube composites (TS-PtCoCu/CNTs), without the need for a reducing agent or surfactant. The TS-PtCoCu/CNTs with optimal Pt content (∼15 %) exhibited excellent EOR activity, with mass and specific activity of 3.58 A mgPt-1 and 5.79 mA cm-2, respectively, which are 3.8 and 13.5 times higher than those of Pt/C. Compared with the control prepared through the traditional furnace annealing, the catalyst also showed excellent activity and stability. DFT calculations revealed that the TS-PtCoCu/CNTs possesses a downshifted d-band center, weakened CO adsorption and higher OH affinity compared with monometallic Pt, all of which lead to the preferred C1 pathway for EOR. This study demonstrates an ultrafast construction of a highly efficient Pt-Co-Cu ternary catalyst for EOR. Additionally, it provides insights into the reaction mechanism based on structural characterization, electrochemical characterization, and theoretical calculations.

Single-Atom Catalysts and Dual-Atom Catalysts for CO2 Electroreduction: Competition or Cooperation?

Developing highly active and selective electrocatalysts for electrochemical reduction of CO2 can reduce environmental pollution and mitigation of greenhouse gas emission. Owing to maximal atomic utilization, the atomically dispersed catalysts are broadly adopted in CO2 reduction reaction (CO2 RR). Dual-atom catalysts (DACs), with more flexible active sites, distinct electronic structures, and synergetic interatomic interactions compared to single-atom catalysts (SACs), may have great potential to enhance catalytic performance. Nevertheless, most of the existing electrocatalysts have low activity and selectivity due to their high energy barrier. Herein, 15 electrocatalysts are explored with noble metallic (Cu, Ag, and Au) active sites embedded in metal-organic hybrids (MOHs) for high-performance CO2 RR and studied the relationship between SACs and DACs by first-principles calculation. The results indicated that the DACs have excellent electrocatalytic performance, and the moderate interaction between the single- and dual-atomic center can improve catalytic activity in CO2 RR. Four among the 15 catalysts, including (CuAu), (CuCu), Cu(CuCu), and Cu(CuAu) MOHs inherited a capability of suppressing the competitive hydrogen evolution reaction with favorable CO overpotential. This work not only reveals outstanding candidates for MOHs-based dual-atom CO2 RR electrocatalysts but also provides new theoretical insights into rationally designing 2D metallic electrocatalysts.

The Transport of Charged Molecules across Three Lipid Membranes Investigated with Second Harmonic Generation.

Subtle variations in the structure and composition of lipid membranes can have a profound impact on their transport of functional molecules and relevant cell functions. Here, we present a comparison of the permeability of bilayers composed of three lipids: cardiolipin, DOPG (1,2-dioleoyl-sn-glycero-3-phospho-(1'-rac-glycerol), and POPG (1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1'-rac-glycerol)). The adsorption and cross-membrane transport of a charged molecule, D289 (4-(4-diethylaminostyry)-1-methyl-pyridinium iodide), on vesicles composed of the three lipids were monitored by second harmonic generation (SHG) scattering from the vesicle surface. It is revealed that structural mismatching between the saturated and unsaturated alkane chains in POPG leads to relatively loose packing structure in the lipid bilayers, thus providing better permeability compared to unsaturated lipid bilayers (DOPG). This mismatching also weakens the efficiency of cholesterol in rigidifying the lipid bilayers. It is also revealed that the bilayer structure is somewhat disturbed by the surface curvature in small unilamellar vesicles (SUVs) composed of POPG and the conical structured cardiolipin. Such subtle information on the relationship between the lipid structure and the molecular transport capability of the bilayers may provide clues for drug development and other medical and biological studies.

F···Br and F···S Heterohalogen-Bond-Directed 2D Self-Assemblies of a Benzothiadiazole Derivative.

Halogen bonding (XB) is of great importance in fabricating a two-dimensional (2D) self-assembly for its adaptive directionality. However, the XBs involving fluorine (F) have barely been studied due to the absence of an σ-hole on F. Here, 2D self-assemblies of a F-substituted 4,7-bis(5-bromo-4-dodecylthiophen-2-yl)-5,6-difluorobenzo[c][1,2,5]thiadiazole (BTZ-BrF) molecule on graphite were investigated using scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. STM experiments revealed that the 2D patterns of BTZ-BrF had a clear solvent and concentration dependence, showing a frame-like pattern in aliphatic acid and aliphatic hydrocarbon solvents at high concentrations. At lower concentrations, a bamboo-like and a wave-like pattern were observed in aliphatic acid, whereas small frame-like and large ladder-like domains at high solution concentrations in aliphatic hydrocarbon were observed. As the concentration further decreased, two linear patterns were observed. DFT calculations suggested that the hetero-XBs of F···Br, F···S, Br···S, and Br···N, the homo-XBs of type-II Br···Br, and the S···S interactions synergistically directed and stabilized the polymorphic 2D architectures. This understanding of intermolecular XBs during the molecular assembly at the molecular level may shed light on the ongoing efforts of regulating nanostructures of multifunctional organics.

Ultrarapid Nanomanufacturing of High-Quality Bimetallic Anode Library toward Stable Potassium-Ion Storage.

Bimetallic alloy nanomaterials are promising anode materials for potassium-ion batteries (KIBs) due to their high electrochemical performance. The most well-adopted fabrication method for bimetallic alloy nanomaterials is tube furnace annealing (TFA) synthesis, which can hardly satisfy the trade-off among granularity, dispersity and grain coarsening due to mutual constraints. Herein, we report a facile, scalable and ultrafast high-temperature radiation (HTR) method for the fabrication of a library of ultrafine bimetallic alloys with narrow size distribution (≈10-20 nm), uniform dispersion and high loading. The metal-anchor containing heteroatoms (i.e., O and N), ultrarapid heating/cooling rate (≈103  K s-1 ) and super-short heating duration (several seconds) synergistically contribute to the successful synthesis of small-sized alloy anodes. As a proof-of-concept demonstration, the as-prepared BiSb-HTR anode shows ultrahigh stability indicated by negligible degradation after 800 cycles. The in situ X-ray diffraction reveals the K+ storage mechanism of BiSb-HTR. This study can shed light on the new, rapid and scalable nanomanufacturing of high-quality bimetallic alloys toward extended applications of energy storage, energy conversion and electrocatalysis.

One-pot synthesis of ultrafine trimetallic PtPdCu alloy nanoparticles decorated on carbon nanotubes for bifunctional catalysis of ethanol oxidation and oxygen reduction.

Bifunctional catalysts for ethanol oxidation reaction (EOR) and oxygen reduction reaction (ORR) with high noble-metal utilization are highly beneficial to direct ethanol fuel cells (DEFCs). This study developed a ternary bifunctional catalyst composed of ultrafine PtPdCu alloy nanoparticles and carbon nanotubes (CNTs) support through a facile surfactant-free solvothermal route. The carboxyl terminal groups on CNTs ensure the confined growth of PtPdCu alloys (∼5 nm) and suppress Ostwald ripening of metallic active sites during electrochemical cycling. Consequently, PtPdCu/CNTs exhibits high mass activity (1.95 A mg-1) and specific activity (4.08 mA cm-2) toward EOR, which are 7.8 and 8.9 times higher, respectively, than those of commercial Pt/C. Furthermore, PtPdCu/CNTs displays superior stability toward EOR compared with its bimetallic counterparts (PtPd/CNTs and PtCu/CNTs). In addition, PtPdCu/CNTs exhibits the highest half-wave potential of 0.888 V among all electrocatalysts, indicating high ORR activity. Density functional theory calculations reveal that Pd and Cu mediate the electronic structure of Pt, leading to enhanced catalytic activity of PtPdCu/CNTs. The excellent catalytic property of PtPdCu/CNTs can also be attributed to the bifunctional effects of Pd/Cu and the interaction between metal and the carbon support. The proposed material is a contribution to the family of efficient ternary-alloy electrocatalysts for fuel cells.

A Novel Hierarchical Structure of SnCu2Se4/d-Ti3C2Tx/NPC for a Lithium/Sodium Ion Battery and Hybrid Capacitor with Long-Term Cycling Stabilities.

To alleviate kinetics imbalance and capacity insufficiency simultaneously, a novel hierarchical structure (SnCu2Se4/d-Ti3C2Tx/NPC) composed of delaminated Ti3C2Tx, SnCu2Se4 nanoparticles, and N-doped porous carbon layers is designed as a battery-type anode for lithium/sodium ion hybrid capacitor (LIC/SIC). The combination of SnCu2Se4 nanoparticles with high specific capacity, d-Ti3C2Tx with accelerated ion diffusion path, and NPC with enhanced electronic conductivity makes the SnCu2Se4/d-Ti3C2Tx/NPC composite possess excellent cycling stabilities in half-cell lithium-ion and sodium-ion batteries (LIB and SIB), with capacities of 114 mAh g-1 after 6000 cycles at 10 A g-1 for LIB and 296 mAh g-1 after 900 cycles at 1.0 A g-1 for SIB. The rate performance is also outstanding, with recovered capacity of 738 mAh g-1 at 0.1 A g-1 after cycles at current densities up to 50 A g-1 for LIB. Subsequently, LIC and SIC based on the SnCu2Se4/d-Ti3C2Tx/NPC anode and activated carbon cathode exhibit high energy densities of 147.9 and 158.6 Wh kg-1 at a power density of 100 W kg-1, respectively. They also possess distinctive long lifespans with capacity retentions of 78 and 81% after 10,000 cycles at 1.0 A g-1, respectively, demonstrating the feasibility of SnCu2Se4/d-Ti3C2Tx/NPC toward energy devices requiring high energy density, power density, and long-term stability.

Probing catalytic reduction on the surface of Au nanoparticles by second-harmonic generation and two-photon luminescence.

The catalytic reduction of aromatic nitro compounds by metallic nanoparticles in the presence of sodium borohydride (NaBH4) has been widely studied as model reactions. However, the reaction mechanisms still need further investigations. For example, the origin of the induction time that has often been observed is still controversial. Here, we demonstrated that such catalytic reduction reactions on the surface of colloidal gold nanoparticles (AuNPs) may be inspected by the second-harmonic generation (SHG) and two-photon luminescence (TPL) emission from AuNPs. It was revealed that the SHG and TPL signals from AuNPs were sensitive to the substitution of citrate by active hydride species derived from the hydrolysis of NaBH4. Based on the UV-vis spectroscopy analyses and monitoring the SHG/TPL signals, the induction time in the catalytic reaction of 4-nitrothiophenol was revealed to originate from the hindered adsorption of hydride on the gold surface. This work demonstrated that SHG and TPL can provide a new approach for detecting active hydrides on the surface of metallic nanoparticles in colloids.

Combined Second Harmonic Generation and Fluorescence Analyses of the Structures and Dynamics of Molecules on Lipids Using Dual-Probes: A Review.

Revealing the structures and dynamic behaviors of molecules on lipids is crucial for understanding the mechanism behind the biophysical processes, such as the preparation and application of drug delivery vesicles. Second harmonic generation (SHG) has been developed as a powerful tool to investigate the molecules on various lipid membranes, benefiting from its natural property of interface selectivity, which comes from the principle of even order nonlinear optics. Fluorescence emission, which is in principle not interface selective but varies with the chemical environment where the chromophores locate, can reveal the dynamics of molecules on lipids. In this contribution, we review some examples, which are mainly from our recent works focusing on the application of combined spectroscopic methods, i.e., SHG and two-photon fluorescence (TPF), in studying the dynamic behaviors of several dyes or drugs on lipids and surfactants. This review demonstrates that molecules with both SHG and TPF efficiencies may be used as intrinsic dual-probes in plotting a clear physical picture of their own behaviors, as well as the dynamics of other molecules, on lipid membranes.

Understanding the different cross-membrane transport kinetics of two charged molecules on the DOPG lipid surface with second harmonic generation and MD simulation.

A clear physical picture of the dynamic behavior of molecules on the surface of the lipid membrane is highly desired and has attracted great attention from researchers. In this study, a step forward in this direction based on previous studies was presented with second harmonic generation (SHG) and molecular dynamic (MD) simulation. Specifically, details on the orientation flipping and cross-membrane transport of two charged molecules, 4-(4-diethylaminostyry)-1-methyl-pyridinium iodide (D289) and malachite green (MG), on the surface of 2-dioleoyl-sn-glycero-3-phospho-rac-(1-glycerol) sodium salt (DOPG) lipids were presented. Firstly, the orientation flipping of the two molecules on the surface of lipids before their cross-membrane transport was confirmed by the MD simulation. Then, the concentration dependent rate of the cross membrane transport for MG/D289 was analyzed. It was found that a simplified model could satisfactorily interpret the faster cross-membrane transport of MG under higher bulk concentrations. A different concentration dependent dynamics was observed with D289 and the reason behind it was also discussed. With this investigation, the surface structures and dynamics of D289 and MG on the DOPG lipid surface were clearly presented.

Revealing the mechanisms of vesicle formation with multiple spectral methods.

The investigation of the self-assembly of amphiphilic molecules and the formation of micelles/vesicles has attracted significant attention. However, in situ and real-time methods for such studies are rare. Here, a surface-sensitive second harmonic generation (SHG) technique was applied to study the formation of vesicles in solutions of an anti-cancer drug, doxorubicin (DOX), and a generally used surfactant (sodium bis (2-ethylhexyl) sulfosuccinate, AOT). With the aid of two-photon fluorescence (TPF), Rayleigh scattering and TEM, we revealed the structural evolution of the aggregated micelles/vesicles. It was found that AOT and DOX molecules rapidly aggregated and formed micelles in the solution. The residual DOX then acted as a "glue" that induced the aggregating/growing of the micelles and the transformation from aggregates to vesicles. The existence of lipid films, which was considered as the necessary intermediate state for vesicle formation, was excluded via the SHG observations, indicating that hollow shells may be directly transformed from solid aggregated micelles in the self-assembly formation of complex vesicles. The combined spectroscopic methods were also used to investigate the formation of vesicles from a commonly used lipid (i.e., 1,2-dioleoyl-sn-glycero-3-phospho-rac-(1-glycerol) sodium salt, DOPG) from its stacked bilayers. The swelling, curving and sealing of the DOPG bilayers for vesicle formation was monitored and clear dynamics were revealed. This work shows that the vesicle formation mechanism varies with the initial state of the surfactant/lipid molecules. It not only demonstrates the capability of the combined spectroscopic methods in investigating the aggregated systems but also provides new insight for understanding the formation of vesicles.

Exploiting the Synergistic Electronic Interaction between Pt-Skin Wrapped Intermetallic PtCo Nanoparticles and Co-N-C Support for Efficient ORR/EOR Electrocatalysis in a Direct Ethanol Fuel Cell.

The development of low-Pt catalysts with high activity and durability is critical for fuel cells. Here, Pt-skin wrapped sub-5 nm PtCo intermetallic nanoparticles are successfully mounted on single atom Co-N-C support by exploiting the barrier effect of Co-anchor. According to a collaborative experimental and computational investigation, the increased oxygen reduction reaction activity of PtCo/Co-N-C arises from the direct electron transfer from PtCo to Co-N-C, and the resulting optimal d-band center of Pt. Owing to such unique electronic structure interaction and synergistic effect, the specific and mass activities of PtCo/Co-N-C are up to 4.20 mA cm-2 and 2.71 A mgPt-1 , respectively, with barely degraded stability after 40 000 CV cycles. The PtCo/Co-N-C also exhibits outstanding activity as an ethanol electrocatalyst. This work shows a new and effective route to boost the overall efficiency of direct ethanol fuel cells in acidic media by integrating intermetallic low-Pt alloys and single atom carbon support.

Theoretically Revealed and Experimentally Demonstrated Synergistic Electronic Interaction of CoFe Dual-Metal Sites on N-doped Carbon for Boosting Both Oxygen Reduction and Evolution Reactions.

Heteronuclear double-atom catalysts, unlike single atom catalysts, may change the charge density of active metal sites by introducing another metal single atom, thereby modifying the adsorption energies of reaction intermediates and increasing the catalytic activities. First, density functional theory calculations are used to figure out the best combination by modeling two transition-metal atoms from Fe, Co, and Ni onto N-doped graphene. Generally, Fe and Co sites are highly active for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER), respectively. The combination of Co and Fe to form CoFe-N-C not only further improves the Fe's ORR and Co's OER activities but also greatly enhances the Co site's ORR and Fe site's OER activities. Then, we synthesize the CoFe-N-C by a two-step pyrolysis process and find that the CoFe-N-C exhibits exceptional ORR and OER electrocatalytic activities in alkaline media, significantly superior to Fe-N-C and Co-N-C and even commercial catalysts.

Evaluating the cross-membrane dynamics of a charged molecule on lipid films with different surface curvature.

Does the curvature of a phospholipid membrane influence the permeability of the lipid bilayers? This is a question of great importance yet hard to answer. In this work the permeability of a positively charged rod like probing molecule (D289 dye) on the bilayers of DOPG lipid vesicles was investigated using angle resolved second harmonic generation method. It was revealed that the permeability of D289 on the surface of small vesicles with âˆ¼ 100 nm diameter was notably lower than that on giant vesicles with âˆ¼ 1000 nm diameter. With the increasing of temperature or the introducing of dimethyl sulfoxide (DMSO) in the solutions, the D289 permeability of the lipid bilayers was notably enhanced as expected, on both the small and the giant vesicles. Still, the D289 permeability of the lipid film with more curvature is lower than the relatively flat film in all these cases. This work demonstrated a general protocol for the investigating of surface permeability of lipid films with various curvature.

MOF Structure Engineering to Synthesize CoNC Catalyst with Richer Accessible Active Sites for Enhanced Oxygen Reduction.

Single-atom cobalt-based CoNC are promising low-cost electrocatalysts for oxygen reduction reaction (ORR). However, further increasing the single cobalt-based active sites and the ORR activity remain a major challenge. Herein, an acetate (OAc) assisted metal-organic framework (MOF) structure-engineering strategy is developed to synthesize hierarchical accordion-like MOF with higher loading amount and better spatial isolation of Co and much higher yield when compared with widely reported polyhedron MOF. After pyrolysis, the accordion-structured CoNC (CoNC (A)) is loaded with denser CoN4 active sites (Co: 2.88 wt%), approximately twice that of Co in the CoNC reported. The presence of OAc in MOF also induces the generation of big pores (5-50 nm) for improving the accessibility of active sites and mass transfer during catalytic reactions. Consequently, the CoNC (A) catalyst shows an admirable ORR activity with a E1/2 of 0.89 V (40 mV better than Pt/C) in alkaline electrolytes, outstanding durability, and absolute tolerance to methanol in both alkaline and acidic media. The CoNC-based Zn-air battery exhibits a high specific capacity (976 mAh g-1 Zn ), power density (158 mW cm-2 ), rate capability, and long-term stability. This work demonstrates a reliable approach to construct single atom doped carbon catalysts with denser accessible active sites through MOF structure engineering.

Unveiling the Molecular Dynamics in a Living Cell to the Subcellular Organelle Level Using Second-Harmonic Generation Spectroscopy and Microscopy.

Second-harmonic generation (SHG) microscopy has been proved to be a powerful method for investigating the structures of biomaterials. SHG spectra were also generally used to probe the adsorption and cross-membrane transport of molecules on lipid bilayers in situ and in real time. In this work, we applied SHG and two-photon fluorescence (TPF) spectra to investigate the dynamics of an amphiphilic ion with an SHG and TPF chromophore, D289 (4-(4-diethylaminostyry)-1-methyl-pyridinium iodide), on the surface of human chronic myelogenous leukemia (K562) cells and the subcellular structures inside the cells. The adsorption and cross-membrane transport of D289 into the cells and then into the organelles such as mitochondria were revealed. SHG images were also recorded and used to demonstrate their capability of probing molecular dynamics in organelles in K562 cells. This work demonstrated the first SHG investigation of the cross-membrane transport dynamics on the surface of subcellular organelles. It may also shed light on the differentiation of different types of subcellular structures in cells.

Photocatalytic redox on the surface of colloidal silver nanoparticles revealed by second harmonic generation and two-photon luminescence.

The redox of silver on the surface of Ag nanoparticles (AgNPs) has received extensive attention because of its significant impact on the biological, physical and chemical properties of AgNPs and their applications. Here we demonstrate that the surface redox reaction of AgNPs in colloids may be investigated by the second harmonic generation (SHG) and two-photon luminescence (TPL) emission from the AgNPs. It was revealed that the oxidation of silver on the surface of AgNPs was accelerated upon femtosecond laser excitation, accompanied by a decrease in the SHG and TPL emissions from the AgNPs. The photon-induced reduction of oxidized silver on AgNPs and the formation of surface defects were also revealed by the changes in the SHG and TPL emissions. Size and morphology changes have not been detected by dynamic light scattering and TEM measurements. The changes in the UV-vis extinction spectra were also very weak compared with previous reports. However, the occurrence of redox reactions on the Ag surface upon femtosecond laser irradiation has been confirmed by multiple control experiments. This work demonstrates that SHG and TPL can sensitively probe the subtle structural change on the surface of AgNPs.