State-specific Detection Research Articles

Oxidation state-specific fluorescent copper sensors reveal oncogene-driven redox changes that regulate labile copper(II) pools

Copper is an essential metal nutrient for life that often relies on redox cycling between Cu(I) and Cu(II) oxidation states to fulfill its physiological roles, but alterations in cellular redox status can lead to imbalances in copper homeostasis that contribute to cancer and other metalloplasias with metal-dependent disease vulnerabilities. Copper-responsive fluorescent probes offer powerful tools to study labile copper pools, but most of these reagents target Cu(I), with limited methods for monitoring Cu(II) owing to its potent fluorescence quenching properties. Here, we report an activity-based sensing strategy for turn-on, oxidation state-specific detection of Cu(II) through metal-directed acyl imidazole chemistry. Cu(II) binding to a metal and oxidation state-specific receptor that accommodates the harder Lewis acidity of Cu(II) relative to Cu(I) activates the pendant dye for reaction with proximal biological nucleophiles and concomitant metal ion release, thus avoiding fluorescence quenching. Copper-directed acyl imidazole 649 for Cu(II) (CD649.2) provides foundational information on the existence and regulation of labile Cu(II) pools, including identifying divalent metal transporter 1 (DMT1) as a Cu(II) importer, labile Cu(II) increases in response to oxidative stress induced by depleting total glutathione levels, and reciprocal increases in labile Cu(II) accompanied by decreases in labile Cu(I) induced by oncogenic mutations that promote oxidative stress.

Narrow-line imaging of single strontium atoms in shallow optical tweezers

Single strontium atoms held in optical tweezers have so far only been imaged using the broad ${}^{1}{S}_{0}{\text{\ensuremath{-}}}^{1}{P}_{1}\phantom{\rule{0.16em}{0ex}}$transition. For Yb, use of the narrow (183-kHz wide) ${}^{1}{S}_{0}{\text{\ensuremath{-}}}^{3}{P}_{1}\phantom{\rule{0.16em}{0ex}}$transition for simultaneous imaging and cooling has been demonstrated in tweezers with a magic wavelength for the imaging transition. We demonstrate high-fidelity imaging of single Sr atoms using its even narrower (7.4-kHz wide) ${}^{1}{S}_{0}{\text{\ensuremath{-}}}^{3}{P}_{1}\phantom{\rule{0.16em}{0ex}}$transition. The atoms are trapped in nonmagic-wavelength tweezers. We detect the photons scattered during Sisyphus cooling, thus keeping the atoms near the motional ground state of the tweezer throughout imaging. The fidelity of detection is 0.9991(4) with a survival probability of 0.97(2). An atom in a tweezer can be held under imaging conditions for 79(3) seconds allowing for hundreds of images to be taken, limited mainly by background gas collisions. The use of a fully closed (cycling) transition for imaging will provide a useful tool for state specific detection. We detect atoms in an array of 36 tweezers with 813.4-nm light and trap depths of 135(20) $\ensuremath{\mu}$K. This trap depth is three times shallower than typically used for imaging on the broad ${}^{1}{S}_{0}{\text{\ensuremath{-}}}^{1}{P}_{1}\phantom{\rule{0.16em}{0ex}}$transition. Narrow-line imaging opens the possibility to even further reduce this trap depth, as long as all trap frequencies are kept larger than the imaging transition linewidth. Imaging using a narrow-linewidth transition in a nonmagic-wavelength tweezer also allows for selective imaging of a given tweezer. As a demonstration, we selectively image (hide) a single tweezer from the array. This provides a useful tool for quantum error correction protocols.

Fluorescence Probing Live Single-cell Mass Spectrometry for Direct Analysis of Organelle Metabolism.

Mitochondria in a live HepG2 cell were visualized with a fluorescent probe to specify their location and state in a living cell. Then, mitochondria were selectively captured with a nanospray tip under fluorescence microscope, and thousands of small molecular peaks were revealed and unique steroids specific to mitochondria were also found. This fluorescence imaging combined with live single-cell mass spectrometry opens the door to the analysis of site- and state-specific molecular detection to elucidate precise molecular mechanisms at the single-cell and organelle level.

Excitation of Sodium Atoms Attached to Helium Nanodroplets: The 3p ← 3s Transition Revisited

The dynamics of Na atoms on the surface of helium nanodroplets following excitation via the 3p ← 3s transition has been investigated using state-specific ion-based detection of the products. Excitation of the system to the 3p (2)Π states is found to lead to the desorption of both bare Na and NaHe exciplexes. The associated speed distributions point to an impulsive desorption process for Na products and a thermally driven process for the NaHe exciplexes. In contrast, excitation of the 3p (2)Σ state leads exclusively to the impulsive desorption of Na atoms. In this case, the desorption is accompanied by a helium-induced relaxation process, as evidenced by the large fraction of detected Na (2)P1/2 atoms. The relaxation process is thought to be related to a crossing between the (2)Π1/2 and (2)Σ potential energy curves at large distance.

Gas-phase diagnoses in catalytic chemical vapor deposition (hot-wire CVD) processes

Radical species play key roles in chemical vapor deposition (CVD) processes, including catalytic CVD (hot-wire CVD), and evaluating their densities in the gas phase is important in understanding the underlying mechanisms and controlling the processes. There are many diagnosis techniques to detect radical species. Among them, photon-in–photon-out techniques, including one- and two-photon laser-induced fluorescence and photo-absorption, can be utilized under the low vacuum conditions typical in CVD processes. Highly sensitive, quantitative, state-specific, real-time, and non-intrusive detection is possible with these techniques; even spatial resolution can be obtained in some cases. At the same time, however, we should know the drawbacks and the limitations of such techniques. A compilation of the radical species detected so far in catalytic CVD processes is presented in a table.

State-specific detection of trapped HfF+ by photodissociation

We use (1+1′) resonance-enhanced multiphoton photodissociation (REMPD) to detect the population in individual rovibronic states of trapped HfF+ with a single-shot absolute efficiency of 18%, which is over 200 times better than that obtained with fluorescence detection. The first photon excites a specific rotational level to an intermediate vibronic band at 35000–36500cm−1, and the second photon, at 37594cm−1 (266nm), dissociates HfF+ into Hf+ and F. Mass-resolved time-of-flight ion detection then yields the number of state-selectively dissociated ions. Using this method, we observe rotational-state heating of trapped HfF+ ions from collisions with neutral Ar atoms. Furthermore, we measure the lifetime of the 3Δ1v=0,J=1 state to be 2.1(2)s. This state will be used for a search for a permanent electric dipole moment of the electron.

Roaming-mediated isomerization in the photodissociation of nitrobenzene

Roaming reactions comprise a new class of reaction in which a molecule undergoes frustrated dissociation to radicals, followed by an intramolecular abstraction reaction. Nitro compounds have long been known to dissociate to give NO as a major product. However, rates based upon isomerization via calculated tight transition states are implausibly slow, so the key dissociation pathway for this important class of molecules remains obscure. Here, we present an imaging study of the photodissociation of nitrobenzene with state-specific detection of the resulting NO products. We observe a bimodal translational energy distribution in which the slow products are formed with low NO rotational excitation, and the fast component is associated with high rotational excitation. High-level ab initio calculations identified a 'roaming-type' saddle point on the ground state. Branching ratio calculations then show that thermal dissociation of nitrobenzene is dominated by 'roaming-mediated isomerization' to phenyl nitrite, which subsequently decomposes to give C(6)H(5)O + NO.

Sequential Multiplex Analyte Capturing for Phosphoprotein Profiling

Microarray-based sandwich immunoassays can simultaneously detect dozens of proteins. However, their use in quantifying large numbers of proteins is hampered by cross-reactivity and incompatibilities caused by the immunoassays themselves. Sequential multiplex analyte capturing addresses these problems by repeatedly probing the same sample with different sets of antibody-coated, magnetic suspension bead arrays. As a miniaturized immunoassay format, suspension bead array-based assays fulfill the criteria of the ambient analyte theory, and our experiments reveal that the analyte concentrations are not significantly changed. The value of sequential multiplex analyte capturing was demonstrated by probing tumor cell line lysates for the abundance of seven different receptor tyrosine kinases and their degree of phosphorylation and by measuring the complex phosphorylation pattern of the epidermal growth factor receptor in the same sample from the same cavity.

STATE-SPECIFIC DETECTION PROBABILITIES AND DISEASE PREVALENCE

Investigations of disease dynamics in wild animal populations often use estimated prevalence or incidence as a measure of true disease frequency. Such indices, almost always based solely on raw counts of infected and uninfected individuals, are often used as the basis for analysis of temporal and spatial dynamics of diseases. Generally, such studies do not account for potential differences in observer detection probabilities of host individuals stratified by biotic and/or abiotic factors. We demonstrate the potential effects of heterogeneity in state-specific detection probabilities on estimated disease prevalence using mark-recapture data from previous work in a House Finch (Carpodacus mexicanus) and Mycoplasma gallisepticum system. In this system, detection probabilities of uninfected finches were generally higher than infected individuals. We show that the magnitude and seasonal pattern of variation in estimated prevalence, corrected for differences in detection probabilities, differed markedly from uncorrected (apparent) prevalence. When the detection probability of uninfected individuals is higher than infected individuals (as in our study), apparent prevalence is negatively biased, and vice versa. In situations where state-specific detection probabilities strongly interact over time, we show that the magnitude and pattern of apparent prevalence can change dramatically; in such cases, observed variations in prevalence may be completely spurious artifacts of variation in detection probability, rather than changes in underlying disease dynamics. Accounting for differential detection probabilities in estimates of disease frequency removes a potentially confounding factor in studies seeking to identify biotic and/or abiotic drivers of disease dynamics. Given that detection probabilities of different groups of individuals are likely to change temporally and spatially in most field studies, our results underscore the importance of estimating and incorporating detection probabilities in estimated disease prevalence (specifically), and more generally, any ecological index used to estimate some parameter of interest. While a mark-recapture approach makes it possible to estimate detection probabilities, it is not always practical, especially at large scales. We discuss several alternative approaches and categorize the assumptions under which analysis of uncorrected prevalence may be acceptable.

Development of a Wet-Chemical Method for the Speciation of Iron in Atmospheric Aerosols

The ability to quantify the chemical and physical forms of transition metals in atmospheric particulate matter (PM) is essential in determining potential human health and ecological effects. A method for the speciation of iron in atmospheric PM has been adapted which involves extraction in a well-defined solution followed by oxidation state specific detection. The method was applied to a suite of environmental aerosols. Ambient atmospheric aerosols in an urban area of St. Louis (the St. Louis-Midwest Supersite) were collected on Teflon substrates and were leached in one of four different solutions: (1) >18.0 Momega water; (2) 140 microM NaCl solution; (3) pH = 7.4 NaHCO3 solution; and (4) pH = 4.3 acetate buffering system. Fe(ll) was determined directly using the Ferrozine method as adapted to liquid waveguide spectrophotometry using a 1 m path-length cell. Fe(lll) was determined similarly after reduction to Fe(ll). It was found that, at low ionic strength, pH exerted a major influence on Fe(ll) solubility with the greatest Fe(ll) concentration consistently found in the pH = 4.3 acetate buffer. Soluble Fe(lll) (as defined by a 0.2 microm filter) varied little with extractant, which implies that most of the Fe(lll) detected was colloidal. To characterize well-defined materials for future reference, NIST standard reference materials were also analyzed for soluble Fe(ll) and Fe(lll). For all SRMs tested, a maximum of 2.4% of the total iron (Urban Dust 1649a) was soluble in pH = 4.3 acetate buffer. For calibration curves covering the ranges of 0.5-20 microg/L Fe(ll), excellent linearity was observed in all leaching solutions with R2 values of > 0.999. Co-located filters were used to test the effect of storage time on iron oxidation state in the ambient particles as a function of time. On two samples, an average Fe(ll) decay rate of 0.89 and 0.57 ng Fe(ll) g(-1) PM day(-1) was determined from the slope of the regression, however this decrease was determined not to be significant over 3 months (95% confidence). As an application of this method to mobile source emissions, size-resolved PM10 samples were collected at the inlet and outlet of the Caldecott Motor Vehicle Tunnel in northern California. These samples indicate that the coarse fraction (PM10-PM2.5) contains almost 50% of the total soluble Fe(ll) in the aerosol.

Photoionization of the primary photoproducts of A(2∏)-excited ClO

Photoionization of the primary photofragments of chlorine monoxide (ClO) is reported. ClO is photolyzed in the X(2∏)→A(2∏)-regime, yielding Cl(2P) and O(3P,1D). The primary photolysis products, as well as the not photolyzed ClO, are subsequently probed by monochromatic, time-correlated vacuum-ultraviolet radiation from a laser produced plasma source. Autoionization is used for state-specific detection of the atomic photolysis products. The formation of O(3P) is exclusively observed above ≈264 nm. The threshold of O(1D) from A(2∏3/2)-excited ClO is found at 263.71±0.01 nm. The shape of the O(1D) yield near this threshold is discussed in terms of the rotational energy distribution and a rotational barrier of A(2∏3/2)-excited ClO. Direct (nonresonant) one-photon-ionization is used to establish the absolute photoionization cross sections of ClO(X(2∏)), Cl(2P), and O(1D) near 15 eV. Additional experiments on the UV-photolysis of Cl2, yielding Cl(2P), are consistent with the results on ClO. The present work is compared to earlier experimental and theoretical studies.

Angular distributions of NO in laser-induced desorption from Pt(111)

The angular distributions of NO photodesorbed from a Pt(111) surface by UV-laser irradiation at 193 nm are investigated as a function of velocity using a quantum state specific detection method, which combines resonance enhanced multiphoton ionization (REMPI) and a two-dimensional-imaging technique. The angular distributions of NO in individual rovibrational states are observed to be strongly peaked in the surface normal direction and are consistently reproduced by gaussian functions in the desorption angle θ. The angular width of these distributions is found to decrease substantially with the velocity of the desorbing molecules. The identical velocity dependence of the angular distributions is observed independent of the rotational quantum states of the photodesorbed NO molecules. This is indicative of a de-coupling of the rotational motion of the molecular axis and the hindered parallel translation of the molecules in the adsorption ground state as well as in the excited states probed by the desorption process. The implications of a simple impulsive model, which relates the amplitude of the frustrated translational motion to the velocity dependence of the observed angular distributions, are discussed.

Photodissociation of S 2Cl 2: state-specific detection of atomic and molecular sulphur

Disulphur dichloride (S 2Cl 2) is dissociated by tunable laser radiation in the region of 36000 to 41500 cm −1. By using LIF and REMPI TOF detection techniques, state-resolved detection is achieved for both products, S 2 and S. In the case of the S 2 molecule, information on relative vibrational and rotational distributions is obtained. Both internal degrees of freedom are characterized by Boltzmann-type distributions, with temperatures of T rot=1000(500) K and T vib=450(100) K. Knowledge of these distributions allows a reconstruction of the state-independent relative S 2 yield in the investigated region. Similarly, relative yield measurements for S are performed for a second dissociation channel. For both channels, energy-dependent absolute cross sections are derived which result in excellent agreement between the combined yield of both channels and the total absorption spectrum of the S 2Cl 2 parent molecule between 36000 and 39000 cm −1. For higher energies, the absorption signal significantly exceeds the overall yield of the S 2- and S-producing channels, thus revealing that further channels open in that region. An overview regarding the dissociation products of S 2Cl 2 is presented for the energy region between 28000 and 41500 cm −1. Features appearing on the low-energy edge of the experimental atomic sulphur yield spectra are analyzed and interpreted in terms of transition state theory.

Vibrational excitation dynamics in photodesorption

Quantum state specific detection of photodesorbed molecules enables measuring their final state distributions in the translational and internal degrees of freedom, which contain a wealth of information about the desorption mechanism and dynamics. Vibrational state populations are of particular interest because of the information they contain about the lifetime and nature of the electronic excited states responsible for desorption. The measured vibrational distributions for nondissociative photodesorption of diatomic molecules tend to resemble Boltzmann distributions with temperatures of 600–1200 K for desorption from metal surfaces, and 1700–2000 K for semiconductors and oxides. Two-dimensional quantum dynamics calculations of the desorption process show that these vibrational distributions can be reproduced only if the intramolecular equilibrium bondlength in the electronic excited state is remarkably similar to that of the ground state. In particular, the results are inconsistent with a desorption mechanism in which the intramolecular bondlength change upon excitation is similar to that of electron capture in the gas phase.

Measurements of long atomic lifetimes at an ion storage ring

Millisecond lifetimes of excited levels in multicharged ions may be measured at ion storage rings. At the Heidelberg ion storage ring TSR, particle detection after collisions between the circulating ions and electrons of the cooler has been used to obtain dielectronic recombination spectra as well as time curves of ionization and recombination for four-electron ions, with the aim of measuring transition probabilities for magnetic dipole and for electric dipole intercombination decays. The measurements on the 2s2p3P1o level in the Be-like ions of N and O indicate lifetime values of Τ=(1.6±0.2) ms for N3+ and of Τ=(0.5±0.1) ms for O4+. Problems of these experiments are discussed as well as the prospects for improved measurements on other such ions of astrophysical interest, planning for state-specific optical detection.

Internal quantum state distributions of NH3 photodesorbed from Cu(111) at 6.4 eV

Abstract The UV photodesorption (6.4 eV) of ammonia from Cu(111) has been investigated using resonance enhanced multiphoton ionization through the B«rrX transition for state specific detection. We have measured the relative populations of both inversion doublet states of the first three vibrational levels in the v 2 mode and the rotational excitation of photodesorbed NH 3 . The average energy content in the v 2 mode corresponds to a temperature of T v 2 = 1000 K which is significantly larger than the translational energy released normal to the surface Ě E trans > 2k = 600 K . A marked underpopulation of the antisymmetric v 2 levels has been observed. The rotations can be described by a Boltzmann distribution with a temperature close to the surface temperature indicating that the molecules do not experience significant torque during the desorption process. No pronounced correlation effects in the population of different degrees of freedom are found. These experimental results are consistent with the assumption that the energy required for desorption is transferred from the initial electronic excitation to the molecule-surface bond via the intramolecular coordinate v 2 .

Multiphoton ionization and chemical dynamics

Abstract Multiphoton ionization spectroscopy is a tool for the elucidation of the structure of high-energy states of atoms and molecules. Particularly when used in combination with time-of-flight mass spectrometry and photoelectron spectroscopy, the range of applications include pure spectroscopic studies, the quantum state specific detection of reactants and products and the preparation of quantumstate-selected reactants for chemical reactivity studies. As such, the techniques have become ubiquitous in the field of chemical reaction dynamics. This paper is concerned mainly with the describing the range of these applications and techniques and a selection of typical results.

Electronic fine structure transitions and rotational energy transfer of NO(X 2Π) in collisions with He: A counterpropagating beam study

The collision dynamics of NO(X 2Π) with He is investigated at a collision energy of 147 meV using the method of counterpropagating pulsed molecular beam scattering. One-dimensional product velocity distributions are determined through ion time-of-flight analysis. State specific detection of NO is achieved through (2+1) resonance enhanced multiphoton ionization detection via the E 2Σ+ intermediate state. Calculated frequencies and line strength factors for the two-photon transition enable the extraction of state resolved degeneracy averaged integral and differential cross sections. The overall behavior of the integral cross sections for fine structure conserving and changing transitions, weighted by the degeneracy of the final state, is well described by two different exponential energy gap laws. Differential cross sections for both types of transitions exhibit very different rotational rainbow structures. For the multiplet changing transition, the scaling law suggests an increased energy transfer efficiency while the rotational rainbow structure indicates a larger effective anisotropy. Therefore, the dynamics at the probed collision energy is clearly dominated by fine structure changing collisions when magnetic sublevel specific cross sections for a specified energy transfer are compared.

Counterpropagating pulsed molecular beam scattering of NH3–Ar. I. State resolved integral cross sections

A new approach to molecular beam scattering is described. The method uses counterpropagating molecular beam pulses to define a scattering geometry of cylindrical symmetry while resonance enhanced multiphoton ionization is applied for the state specific product detection. The simple correlation of laboratory and center-of-mass quantities allows a straightforward determination of differential cross sections from measured ion time-of-flight distributions. In addition, the short duration of the pulses causes a delay dependence of the scattering signal which is used as an additional control parameter to define the size of the scattering volume. The method is applied to the rotational excitation of NH3 in collisions with Ar at a collision energy of 158 meV. Delay and depletion studies yield an effective mean free path of 60 cm, confirming single collision condition. While parity averaged integral cross sections are determined for the para modification of NH3, fully state resolved integral cross sections are determined for o-NH3. The general behavior of the integral cross sections for both modifications is well described by an exponential energy gap law. Deviations of individual cross sections from the scaling law confirm the propensity for inelastic collisions with Δk=3. Transitions to parity levels, which are forbidden in the centrifugal sudden approximation, show significantly less intensity.

Counterpropagating pulsed molecular beam scattering of NH3–Ar. II. State resolved differential cross sections

State resolved differential cross sections (DCSs) for the rotational excitation of NH3 in collisions with Ar for various final states at a collision energy of 158 meV have been determined in a counterpropagating pulsed molecular beam scattering experiment. Simultaneous state and velocity specific detection of scattered products is achieved through resonance enhanced multiphoton ionization with subsequent ion time-of-flight analysis. The supersonic expansion ensures the preparation of well-defined initial states in both nuclear spin modifications. While measured DCSs for para-NH3 are parity averaged, state resolved cross sections could be determined for ortho-NH3. All DCSs are dominated by small or intermediate angle scattering, indicating the importance of the anisotropy in the long range part of the potential surface. The maxima in the DCSs are shifted towards larger scattering angles with increasing energy transfer, a behavior characteristic of a rotational rainbow. Excitation probabilities to states which are forbidden in the centrifugal sudden approximation are characterized by a significant decrease in intensity in the backward direction as well as a steeper exponential fall off at small angles.