Bimodal Excitation Research Articles

Methods for Monitoring Mitophagy Using mt-Keima.

Mitochondria-targeted Keima (mt-Keima) is a pH-sensitive, acid-stable fluorescent protein used for the quantification of mitophagy. Mt-Keima contains a mitochondrial matrix targeting sequence and has bimodal excitation with peaks at 440nM in neutral environments and 586nM in acidic environments. From this bimodal excitation, a ratiometric signal may be calculated to quantify mitophagy in live cells. This chapter describes procedures for measuring mitophagy by flow cytometry and live cell confocal microscopy with mt-Keima.

3D printed self-calibrating on-site sensing platform based on bimodal excitation carbon dots for visual 4-nitrophenol detection by means of the localization of inner filter effect and pH regulation

For facile and rapid detection of 4-nitrophenol (4-NP), we synthesize nitrogen-doped carbon dots (N-CDs) through microwave radiation treatment using melamine and o-phenylenediamine as precursors. We employed N-CDs as an ingenious ratiometric fluorescence sensor via a novel bimodal excitation behavior. As the concentration of N-CDs increases, the broad excitation peak splits into two excitation peaks. The blue-shift phenomenon appears at the short-wavelength excitation peak, while the long-wavelength excitation peak presents the red-shift. Consequently, 4-NP can be sensitively detected by N-CDs owing to the localization of inner filter effect (L-IFE) with the detection limit of 83 nM ranging from 0.083 to 80 µM. Moreover, a self-calibrating on-site sensing platform constructed by 3D printing technique realizes the visual 4-NP detection in actual samples based on bimodal excitation behavior and RGB analysis. Our work not only presents a novel perspective for visual 4-NP sensing, but also renders the integration of 3D printing technology and the CDs industry.

Innovative linkage sensor based on bimodal excitation behavior nitrogen doped carbon dots for ratiometric and visual detection of fluoride ion in food

Fluoride ion (F−), particularly an important substance for growth, development and bone metabolism, is one of the essential micronutrients in living organisms. Therefore, F− detection becomes one of the main problems that need to be addressed in ordinary living. Herein, an innovative bimodal excitation-based nitrogen-doped carbon dots (N-CDs) for ratiometric detection of fluoride ion (F−) is developed by multistage response to curcumin and F− based on the localization of inner filter effect (L-IFE). Primarily, curcumin decreases the N-CDs fluorescence due to fluorescence resonance energy transfer. Subsequently, the cascade addition of F− changes the absorption band from 526 to 418 nm due to the generation of curcumin-F− complex. Thus, the L-IFE occurs, and uneven overlap between the curcumin-F− complex absorption and N-CDs excitation leads to the inverse variation in fluorescence signals under the illumination of 399 nm and 470 nm. This multistage sensing system exhibits excellent sensitivity toward F−, with a linear range from 0 to 50 µM and a low detection limit of 57 nM. Moreover, a smart-integrated sensing platform is designed for visual F− detection in practical samples. Thus, our work provides a novel guidance for F− detection in food environment.

Aggregation-induced bimodal excitation of nitrogen-doped carbon dots for ratiometric sensing of new coccine and solid-state multicolor lighting

Trace detection of foodstuff pigments have gained increasing attention because of their close association with biological and environmental processes. Herein, we propose an innovative bimodal excitation nitrogen-doped carbon dots (N-CDs) for ratiometric sensing of new coccine (NC) pigment, which are synthesized by using melamine and o-phenylenediamine as precursors via solvothermal treatment. With the increase of the N-CDs concentration, N-CDs exhibit not only a concentration-dependent tunable color behavior, but also a novel aggregation-induced bimodal excitation phenomenon. Considering this distinctive bimodal excitation behavior, a ratiometric sensor based on N-CDs has been developed for the detection of the NC in different organic solvents due to the inner filter effect and fluorescence resonance energy transfer. The intensity ratio of two excitation signals is linear with the NC concentration in the range of 0.032–100 µM, and the limit of detection is as low as 32.1 nM. Meanwhile, we realize the design of multicolor-emission N-CDs/polymer films. All in all, this work presents a novel kind view of the mechanism of distinctive bimodal excitation of N-CDs, and further proposes an innovative ratiometric method for the screening analysis of NC in food samples and environmental pollutants.

Observable responses of micro-cantilever array to dynamic acoustic forces at higher mode in the broadband frequency window

We develop a theoretical framework describing numerical approach to explore dynamic acoustic force sensitivity using micro-cantilever array in monomodal and bimodal operations. The excitation force at the second eigenmode frequency is supplied to the micro-cantilevers in monomodal operation. Since we focus on measurement sensitivity of acoustic forces at higher frequencies, deflections of micro-cantilevers at higher mode, second flexural mode, are obtained. In bimodal operations, external driving forces at the first and second eigenmode frequencies are applied simultaneously for the actuation of micro-cantilevers in an array. Depending on acoustic force strength, the application of driving force at higher eigenmode frequency in bimodal excitation scheme increases the phase sensitivity in measurement of acoustic forces within a particular frequency scope. For both excitation schemes, oscillation observables such as amplitude and phase shift are determined with respect to acoustic force frequencies for diverse acoustic force strengths. Simulation results suggest that wider high-sensitivity frequency band could be acquired, utilizing resonantly excited micro-cantilever array. For our case, we obtain the high-sensitivity frequency band of around 200–270 kHz and 440–570 kHz for the acoustic force strengths in the range of 126–1138.5 pN.

Toxoplasma gondii excretion of glycolytic products is associated with acidification of the parasitophorous vacuole during parasite egress.

The Toxoplasma gondii lytic cycle is a repetition of host cell invasion, replication, egress, and re-invasion into the next host cell. While the molecular players involved in egress have been studied in greater detail in recent years, the signals and pathways for triggering egress from the host cell have not been fully elucidated. A perforin-like protein, PLP1, has been shown to be necessary for permeabilizing the parasitophorous vacuole (PV) membrane or exit from the host cell. In vitro studies indicated that PLP1 is most active in acidic conditions, and indirect evidence using superecliptic pHluorin indicated that the PV pH drops prior to parasite egress. Using ratiometric pHluorin, a GFP variant that responds to changes in pH with changes in its bimodal excitation spectrum peaks, allowed us to directly measure the pH in the PV prior to and during egress by live-imaging microscopy. A statistically significant change was observed in PV pH during ionomycin or zaprinast induced egress in both wild-type RH and Δplp1 vacuoles compared to DMSO-treated vacuoles. Interestingly, if parasites are chemically paralyzed, a pH drop is still observed in RH but not in Δplp1 tachyzoites. This indicates that the pH drop is dependent on the presence of PLP1 or motility. Efforts to determine transporters, exchangers, or pumps that could contribute to the drop in PV pH identified two formate-nitrite transporters (FNTs). Auxin induced conditional knockdown and knockouts of FNT1 and FNT2 reduced the levels of lactate and pyruvate released by the parasites and lead to an abatement of vacuolar acidification. While additional transporters and molecules are undoubtedly involved, we provide evidence of a definitive reduction in vacuolar pH associated with induced and natural egress and characterize two transporters that contribute to the acidification.

Coherent fundamental-harmonic interactions in a compressible shear layer via integral nonlinear instability approach

A physics-based integral approach is adopted here to develop a theory for studying bi-modal excitation of the shear layer of a Mach 1.5 planar jet. The transverse shapes of the mean flow quantities are given by analytical functions modeling the corresponding jet experiment and Reynolds-averaged Navier–Stokes solution. The transverse shapes of the frequency modes of the coherent large-scale structure are obtained as the eigenfunctions of the locally parallel linear stability theory. The Navier–Stokes equations are then reduced to a set of ordinary differential equations. The solution of this set, subject to the initial conditions, describes the nonlinear interaction among the excited frequency modes, as well as their interaction with the mean flow and the background turbulence. Our analysis shows that the time-averaged interaction among the modes is non-zero only if the two frequency modes are related to each other by the fundamental-harmonic frequency. We label the fundamental mode here, “f,” as the most amplified mode developing nonlinearly along the jet in the absence of other imposed modes. We then use the resulting theory to study the effect of bimodal excitation by harmonically related pairs (f, f/2) or (f, 2f) to see under which conditions this bimodal excitation can suppress the fundamental. We found that the combination of fundamental and harmonic (f, 2f) can effectively reduce the fundamental at an optimized phase lag. By viewing the fundamental as the most dominant sound source in the jet, it is, thus, possible to reduce the jet noise via bi-modal excitation.

In Vivo Monitoring of Cytosolic pH Using the Ratiometric pH Sensor pHluorin.

Cytosolic pH (pHcyt) is a key factor controlling cell fate. The genetically encoded pH-sensor pHluorin has proven highly valuable for studies on pHcyt in many living organisms. pHluorin displays a bimodal excitation spectrum with peaks at 395nm and 475nm, which is dependent on pH. Here we describe two different protocols for determining pHcyt in the soil-borne fungal pathogen Fusarium oxysporum, based either on population or single-cell analysis.

Sub-10nm spatial resolution for electrical properties measurements using bimodal excitation in electric force microscopy.

We demonstrate that under ambient and humidity-controlled conditions, operation of bimodal excitation single-scan electric force microscopy with no electrical feedback loop increases the spatial resolution of surface electrical property measurements down to the 5nm limit. This technical improvement is featured on epitaxial graphene layers on SiC, which is used as a model sample. The experimental conditions developed to achieve such resolution are discussed and linked to the stable imaging achieved using the proposed method. The application of the herein reported method is achieved without the need to apply DC bias voltages, which benefits specimens that are highly sensitive to polarization. Besides, it allows the simultaneous parallel acquisition of surface electrical properties (such as contact potential difference) at the same scanning rate as in amplitude modulation atomic force microscopy (AFM) topography measurements. This makes it attractive for applications in high scanning speed AFM experiments in various fields for material screening and metrology of semiconductor systems.

A Sensitive and Quantitative mKeima Assay for Mitophagy via FACS.

Mitophagy is a selective autophagy process that specifically removes damaged mitochondria via general autophagy. The two major recessive Parkinson's disease genes PINK1 and Parkin play essential roles in mitophagy initiation, increasing the interest in mitophagy in both basic and translational research over the past 10 years. Initially, mitophagy was measured by the loss of mitochondria either through confocal imaging or immunoblot of mitochondrial proteins such as Tom20 or COXII. Confocal imaging of mitochondria DNA loss via anti‐DNA staining is another option. All of these methods, which take considerable effort and labor, are not sensitive enough to detect early stages of mitophagy with unambiguous objectivity. The mKeima assay can be used for both confocal imaging and FACS analysis to provide a thorough picture of mitophagy with a wide dynamic range. The Keima fluorophore has bimodal excitation under neutral and acidic pH conditions. Thus, when Keima is targeted to mitochondria it can accurately reveal the formation of mitolysosomes. Here the author briefly describes the origin and history of mKeima and how it is adapted to measure mitophagy. The author presents detailed protocols for making stable cell lines for optimized mitophagy detection and discuss many parameters that might affect the assay. A troubleshooting section is also provided to discuss possible pitfalls to improve reproducibility and sensitivity of the assay. © 2019 The Authors. Basic Protocol 1: Making stable lines expressing mito‐mKeima and YFP‐Parkin Support Protocol: Retrovirus/lentivirus infection Basic Protocol 2: FACS analysis of mitophagy

Spatial Selectivity in Cochlear Implants: Effects of Asymmetric Waveforms and Development of a Single-Point Measure

Three experiments studied the extent to which cochlear implant users’ spatial selectivity can be manipulated using asymmetric waveforms and tested an efficient method for comparing spatial selectivity produced by different stimuli. Experiment 1 measured forward-masked psychophysical tuning curves (PTCs) for a partial tripolar (pTP) probe. Maskers were presented on bipolar pairs separated by one unused electrode; waveforms were either symmetric biphasic (“SYM”) or pseudomonophasic with the short high-amplitude phase being either anodic (“PSA”) or cathodic (“PSC”) on the more apical electrode. For the SYM masker, several subjects showed PTCs consistent with a bimodal excitation pattern, with discrete excitation peaks on each electrode of the bipolar masker pair. Most subjects showed significant differences between the PSA and PSC maskers consistent with greater masking by the electrode where the high-amplitude phase was anodic, but the pattern differed markedly across subjects. Experiment 2 measured masked excitation patterns for a pTP probe and either a monopolar symmetric biphasic masker (“MP_SYM”) or pTP pseudomonophasic maskers where the short high-amplitude phase was either anodic (“TP_PSA”) or cathodic (“TP_PSC”) on the masker’s central electrode. Four of the five subjects showed significant differences between the masker types, but again the pattern varied markedly across subjects. Because the levels of the maskers were chosen to produce the same masking of a probe on the same channel as the masker, it was correctly predicted that maskers that produce broader masking patterns would sound louder. Experiment 3 exploited this finding by using a single-point measure of spread of excitation to reveal significantly better spatial selectivity for TP_PSA compared to TP_PSC maskers.

Inhibitory suppression of heterogeneously tuned excitation enhances spatial coding in CA1 place cells.

Place cells in the CA1 region of the hippocampus express location-specific firing despite receiving a steady barrage of heterogeneously tuned excitatory inputs that should compromise output dynamic range and timing. We examined the role of synaptic inhibition in countering the deleterious effects of off-target excitation. Intracellular recordings in behaving mice demonstrate that bimodal excitation drives place cells, while unimodal excitation drives weaker or no spatial tuning in interneurons. Optogenetic hyperpolarization of interneurons had spatially uniform effects on place cell membrane potential dynamics, substantially reducing spatial selectivity. These data and a computational model suggest that spatially uniform inhibitory conductance enhances rate coding in place cells by suppressing out-of-field excitation and by limiting dendritic amplification. Similarly, we observed that inhibitory suppression of phasic noise generated by out-of-field excitation enhances temporal coding by expanding the range of theta phase precession. Thus, spatially uniform inhibition allows proficient and flexible coding in hippocampal CA1 by suppressing heterogeneously tuned excitation.

A finite strain viscoplastic constitutive model for rubber with reinforcing fillers

A three dimensional viscoplastic constitutive model for finite strains in a co-rotational explicit scheme is developed and implemented using finite elements that captures the amplitude dependency, commonly referred to as the Fletcher-Gent effect, and frequency dependency of rubber with reinforcing fillers. The multiplicative split of the deformation gradient is utilized and the plastic flow rule stems from an extension to finite strains of a boundary surface model with a vanishing elastic region. The storage and loss modulus for a 50 phr carbon black filled natural rubber are captured over a large range of strain amplitudes, 0.2−50% shear strain, and frequencies, 0.2−20 Hz. In addition, bimodal excitation is replicated accurately, even though this measurement data is not included when obtaining material parameters. This capability is essential when non-sinusoidal loading conditions are to be replicated. By separating the material and geometrical influence on the properties of a component, the design engineers have the capability to evaluate more concepts early in the design phase. This also reduces the need of complex prototypes for physical testing, thereby saving both time and money.

Analysis of hysteresis effect on the vibration motion of a bimodal non-uniform micro-cantilever using MCS theory

Nowadays, to enhance the performance of atomic force microscopy (AFM) micro-cantilevers (MCs) during imaging, reduce costs and increase the surface topography precision, advanced MCs equipped with piezoelectric layers are utilized. Using the modified couple stress (MCS) theory not only makes the modeling more exhaustive, but also increases the accuracy of prediction of the vibration behavior of the system. In this paper, Hamilton’s principle by consideration of the MCS theory has been used to extract the equations. In addition, to discretize the equations, differential quadrature method has been adopted. Analysis of the hysteresis effect on the vibration behavior of the AFM MC is of significant importance. Thus, to model the hysteresis effect, Bouc–Wen method, which is solved simultaneously with the vibration equations of non-uniform Timoshenko beam, has been utilized. Furthermore, a bimodal excitation of the MC has been considered. The results reveal that the hysteresis effect appears as a phase difference in the time response. Finally, the effect of the geometric parameters on the vibration frequency of the system which is excited by combination of the first two vibration modes of the non-uniform piezoelectric MC has been examined. The results indicate the considerable effect of the MC length in comparison with other geometric parameters such as the MC width and thickness.

Abstract 15378: Mitochondrial Fission Plays a Crucial Role in Cardiomyocyte Adaptation to Energy Stress via Mitophagy

Mitochondria are dynamic organelles that undergo fusion and fission. This study aims to clarify the role of mitochondrial dynamics on energetic stress resistance in cardiomyocytes (CMs). Dynamin-related protein 1 (Drp-1) which mediates mitochondrial fission was localized primarily in the cytosol in CMs. Glucose deprivation (GD) induced modest mitochondrial accumulation of Drp1 in CMs within 4 hours. Four-hour GD increased the proportion of CMs with fused mitochondria (23.5±6.9 to 35.0±10.8%, p<0.05), but also increased that of CMs with fission (2.1±0.3 to 15.5±4.8%, p<0.05) in Ad-shScr-transduced CMs, whereas mitochondria with fission did not increase after GD in Ad-shDrp1-transduced CMs (0.3±0.6 to 0.8±0.5%). These results suggest that GD induces both mitochondrial fusion and fission, and Drp1 plays an essential role in mitochondrial fission in response to GD. Transduction with Ad-shDrp1 significantly increased TUNEL-positive CMs and reduced cell viability after 4 hours of GD compared to transduction with Ad-shScr, suggesting that endogenous Drp1 protects CMs against cell death during GD. We evaluated the role of Drp1 in mediating mitophagy using mitochondria-targeted Keima fluorescence. Keima has a bimodal excitation spectrum peaking at 440 and 560 nm, corresponding to the neutral and acidic pH states, respectively. Puncta with high 560/440, indicating the presence of mitochondria in lysosomes, were significantly increased after 4 hours of GD in CMs transduced with Ad-shScr, but not in CMs transduced with Ad-shDrp, suggesting that Drp1 is necessary for stimulating autophagic mitochondrial degradation. Next, we examined the role of fission on energy stress in vivo using cardiac specific Drp1 hetero knockout (Drp1-hetCKO) mouse. Translocation of Drp1 from cytosol to mitochondria significantly increased in response to 48-hour fasting in control mice but not in Drp1-hetCKO mice. Left ventricular ejection fraction did not change after fasting in control mice (79.8±6.4 to 78.6±8.3%). However that in Drp1-hetCKO mice decreased after GD (79.4±9.7 to 48.3±11.6%, p<0.05), suggesting that Drp1 acts to preserve cardiac function during fasting. In conclusion, mitochondrial fission is crucial to adapt CMs to energy stress through mitophagy.

Abstract 339: Heterozygous Disruption of Drp1 Enhances Myocardial Injury in Response to Ischemia/Reperfusion via Inhibition of Mitophagy

Mitochondrial fission and fusion are essential for maintaining mitochondrial quality control. However, their role in stress resistance remains unknown. Since Dynamin-related protein 1 (Drp1) plays an essential role in mediating mitochondrial fission, we used cardiac-specific heterozygous Drp1 KO (Drp1-hetCKO) mice whose cardiac function is normal at 12 weeks of age. In order to evaluate the role of Drp1 in mediating stress resistance, 12-week-old Drp1-hetCKO and control (Ctr) mice were subjected to myocardial ischemia (30 min)/reperfusion (24 hours) (I/R). I/R injury increased the translocation of Drp1 from cytosol to mitochondria in Ctr mice, whereas this translocation was attenuated in Drp1-hetCKO mice.The infarct size/area at risk after I/R was significantly greater in Drp-1 hetero KO mice than in control mice (55.2 ± 3.0 vs. 40.2 ± 1.6%). Electron microscopic analyses showed that I/R significantly decreased mitochondrial mass and increased the number of autophagosomes containing mitochondria in control mice. However, these changes were significantly attenuated in Drp1-hetCKO mice, suggesting that endogenous Drp1 mediates mitochondrial fission and mitophagy after I/R (Relative mitochondrial mass, Ctr, baseline: 1.0±0.3, I/R: 0.7±0.4; Drp1-hetCKO, baseline: 1.8±0.3, I/R: 1.7±0.3). We also examined mitophagy using mitochondria-targeted Keima fluorescence. Keima has a bimodal excitation spectrum peaking at 440 and 560 nm, corresponding to the neutral and acidic pH states, respectively. The maturation of autophagosomes to autolysosomes can be monitored by measuring the fluorescence of mitochondria-targeted Keima. Fluorescent dots with high ratios of 560/440, indicating mitophagy, were significantly increased after GD in sh-scramble-transduced CMs (GD: 28.6±4.2, control 2.3±1.0 dots/cell, p<0.01) but not in sh-Drp1-transduced CMs (GD: 2.4±1.8, control 3.2±1.6 dots/cell, not significant), suggesting that GD stimulates mitophagy but that this is inhibited when Drp-1 is downregulated. These results suggest that endogenous Drp1 play an essential role in mediating mitochondrial fission and mitophagy, which in turn play an essential role in mediating myocardial protection in response to I/R.

Abstract 207: Unc-51-like Kinase 1 (ULK1) Plays A Crucial Role In Mitophagy In Cardiomyocytes

The mitochondrion is an essential organelle that supplies ATP in cardiomyocytes (CMs). However, damaged mitochondria are harmful via the production of reactive oxygen species and induction of apoptosis in pathological conditions. Therefore, quality of mitochondria should be controlled tightly through various mitochondrial quality control mechanisms. Mitochondrial autophagy (mitophagy) is considered an integral part of this mechanism, and recent investigations uncovered the role of PINK1 and Parkin in mitophagy. However, these observations were made under artificial conditions, such as over-expression of Parkin or treatment with CCCP, and thus the precise mechanism has not been fully elucidated in more pathophysiologically relevant conditions. Recent evidence suggests that mitophagy can take place independently of ATG7, a molecule essential for the conventional form of autophagy, and that this form of autophagy is ULK1-dependent. We investigated the role of ULK1 and ATG7 in mediating mitophagy using mitochondria-targeted Keima (Mito-Keima) in cultured rat neonatal CMs. Keima has a bimodal excitation spectrum peaking at 440 and 560 nm, corresponding to the neutral and acidic pH, respectively. In CMs transfected with Mito-Keima, the fluorescent dots with a high 560nm/440nm ratio represent the mitochondria incorporated into autolysosomes which indicate mitophagy. Here we report that ULK1 plays a more predominant role in glucose deprivation (GD) -induced mitophagy than ATG7. Control CMs exhibited 8.7±1.0 % of the area of high-ratio dots per cells after GD. Knockdown of ULK1 significantly reduced the area to 2.3±0.9 % in CMs after GD (p<0.01, vs sh-Control). The reduction was significantly greater in CMs with knockdown of ULK1 than that of ATG7 (7.0±1.6 %, p<0.05, sh-ULK1 vs sh-ATG7). In addition, knockdown of Beclin1 and Drp1 also significantly decreased the area of high-ratio dots (about 1.0 % and 0.5 %, respectively). Overexpression of ULK1 was sufficient to induce mitophagy without starvation, whereas that of ATG7 was not. These results suggest that ULK1, Beclin1 and Drp1 play an essential role in mediating GD-induced mitophagy in CMs.

Spread of excitation varies for different electrical pulse shapes and stimulation modes in cochlear implants

In Cochlear Implants (CI) Bipolar (BP) electrical stimulation has been suggested as a method to reduce the spread of current along the cochlea. However, behavioral measurements in BP mode have shown either similar or worse performance than in Monopolar (MP) mode. This could be explained by a bimodal excitation pattern, with two main excitation peaks at the sites of the stimulating electrodes. We measured the Spread of Excitation (SOE) by means of the Electrically Evoked Compound Action Potential (ECAP), obtained using the forward-masked paradigm. The aim was to measure the bimodality of the excitation and to determine whether it could be reduced by using asymmetric pulses. Three types of maskers shapes were used: Symmetric (SYM), Pseudomonophasic (PS), and Symmetric with a long Inter-Phase Gap (SYM-IPG) pulses. Maskers were presented in BP + 9 (wide), BP + 3 (narrow) and MP (only SYM) mode on fixed electrodes. The SOE obtained with the MP masker showed a main excitation peak close to the masker electrode. Wide SYM maskers produced bimodal excitation patterns showing two peaks close to the electrodes of the masker channel, whereas SYM-IPG maskers showed a single main peak near the electrode for which the masker's second phase (responsible for most of the masking) was anodic. Narrow SYM maskers showed complex and wider excitation patterns than asymmetric stimuli consistent with the overlap of the patterns produced by each channel's electrodes. The masking produced by narrow SYM-IPG and PS stimuli was more pronounced close to the masker electrode for which the effective phase was anodic. These results showed that the anodic polarity is the most effective one in BP mode and that the bimodal patterns produced by SYM maskers could be partially reduced by using asymmetric pulses.

Noninvasive Protein Structural Flexibility Mapping by Bimodal Dynamic Force Microscopy

Mapping of the protein structural flexibility with sub-2-nm spatial resolution in liquid is achieved by combining bimodal excitation and frequency modulation force microscopy. The excitation of two cantilever eigenmodes in dynamic force microscopy enables the separation between topography and flexibility mapping. We have measured variations of the elastic modulus in a single antibody pentamer from 8 to 18 MPa when the probe is moved from the end of the protein arm to the central protrusion. Bimodal dynamic force microscopy enables us to perform the measurements under very small repulsive loads (30-40 pN).

Enhanced switching law for synchronized switch damping on inductor with bimodal excitation

Piezoelectric shunt damping is an emerging field of research. In recent years, a multitude of different electrical circuits have been developed aiming to increase the damping performance and robustness. Synchronized switch damping on inductor (SSDI) is a semi-active control technique that utilizes a passive inductance to build-up a voltage on the piezoceramics that is synchronized with the mechanical vibration. For a single mode excitation the voltage inversion should occur at the moments of maximum deformation, but for multimodal vibrations such a switching law may not be optimal. In this paper a novel switching law for bimodal vibrations is presented using a modal observer. An enhanced voltage build-up is generated by utilizing the vibration energy of the second mode. The amplification of dissipated energy is calculated in an analytical way using normalized parameters, yielding a general result which includes the influence of the frequency and amplitude ratio of the excitation signal. Measurements on a clamped beam test rig are conducted in order to validate the proposed method. An increase of nearly 350 percent in energy dissipation compared to the classical SSDI has been achieved. Furthermore, the increase in energy dissipation is higher than for a previously suggested, comparable switching law.