Tjaart P J Krüger

Tjaart P J Krüger
University of Pretoria | UP · Department of Physics

Associate Professor

About

93
Publications
16,625
Reads
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1,380
Citations
Additional affiliations
January 2018 - present
University of Pretoria
Position
  • Professor (Associate)
March 2013 - December 2017
University of Pretoria
Position
  • Professor (Associate)
April 2006 - February 2013
Vrije Universiteit Amsterdam

Publications

Publications (93)
Article
Full-text available
When exposed to intense sunlight all organisms performing oxygenic photosynthesis implement various photoprotective strategies to prevent potentially lethal photodamage. The rapidly responding photoprotective mechanisms, occurring in the light-harvesting pigment-protein antennae, take effect within tens of seconds, while the dramatic and potentiall...
Article
Full-text available
The ability to dissipate large fractions of their absorbed light energy is a vital photoprotective function of the peripheral light-harvesting pigment-protein complexes in Photosystem II of plants. The major component of this process, known as qE, is characterised by the appearance of low-energy (red-shifted) absorption and fluorescence bands. Alth...
Article
In the major peripheral plant light-harvesting complex LHCII, excitation energy is transferred between chlorophylls along an energetic cascade before it is transmitted further into the photosynthetic assembly to be converted into chemical energy. The efficiency of these energy transfer processes involves a complicated interplay of pigment-protein s...
Article
Full-text available
The light-harvesting antenna of photosystem II (PSII) has the ability to switch rapidly between a state of efficient light use and one in which excess excitation energy is harmlessly dissipated as heat, a process known as qE. We investigated the single-molecule fluorescence intermittency of the main component of the PSII antenna (LHCII) under condi...
Article
Full-text available
The light-harvesting complexes of photosystem I and II (Lhcas and Lhcbs) of plants display a high structural homology and similar pigment content and organization. Yet, the spectroscopic properties of these complexes, and accordingly their functionality, differ substantially. This difference is primarily due to the charge-transfer (CT) character of...
Preprint
Full-text available
The accuracy of approximate methods for calculating linear optical spectra depends on many variables. In this study, we fix most of these parameters to typical values found in photosynthetic light-harvesting complexes of plants and determine the accuracy of approximate spectra with respect to exact calculation as a function of the energy gap and in...
Preprint
Full-text available
Real-time feedback-driven single-particle tracking is a technique that uses feedback control to enable single-molecule spectroscopy of freely diffusing particles in native or near-native environments. A number of different RT-FD-SPT approaches exist, and comparisons between methods based on experimental results are of limited use due to differences...
Conference Paper
Full-text available
Based on engaged experience and the recommendations of ICNIRP and the Netherlands (NL) ministry of Health, the growth and evolution to public and scientific resolutions in the domain of native and non-native electromagnetic fields (nnEMF) is easiest and most efficient when persons (schools, citizens, academics, governments) understand electromagnet...
Article
Full-text available
Real‐time feedback‐driven single‐particle tracking (RT‐FD‐SPT) is a class of techniques in the field of single‐particle tracking that uses feedback control to keep a particle of interest in a detection volume. These methods provide high spatiotemporal resolution on particle dynamics and allow for concurrent spectroscopic measurements. This review a...
Article
We develop a theoretical framework, based on a multipole, quasi-static approach, for the prediction of the localized surface plasmon resonances in Fanoshells formed via geometrical symmetry breaking in multilayer nanoshells consisting of a metallic core, a dielectric inner shell, and a metallic outer shell. By tuning the core and shell offsets of a...
Preprint
Full-text available
The African School of Fundamental Physics and Applications, also known as the African School of Physics (ASP), was initiated in 2010, as a three-week biennial event, to offer additional training in fundamental and applied physics to African students with a minimum of three-year university education. Since its inception, ASP has grown to be much mor...
Article
Full-text available
In this study, zinc-doped (α-Fe2O3:Zn), silver-doped (α-Fe2O3:Ag) and zinc/silver co-doped hematite (α-Fe2O3:Zn/Ag) nanostructures were synthesized by spray pyrolysis. The synthesized nanostructures were used as photoanodes in the photoelectrochemical (PEC) cell for water-splitting. A significant improvement in photocurrent density of 0.470 mAcm−2...
Article
Understanding the origin of irreversibility in thermodynamics has been a fundamental scientific challenge and puzzle for nearly a century. Initially, the discussions related to classical thermodynamic systems, but recently quantum systems became the main focus. Explanations have often been sought by reference to classical equations of motion, which...
Preprint
Full-text available
We develop a theoretical framework, based on a multipole, quasi-static approach, for the prediction of the localized surface plasmon resonances in Fanoshells formed via geometrical symmetry-breaking in multilayer nanoshells consisting of a metallic core, a dielectric inner shell, and a metallic outer shell. By tuning the core and shell offsets of a...
Article
Full-text available
Introduction This review addresses metabolic diversities after grain feeding of cattle using artificial total mixed ration (TMR), in place of pasture-based feeding. Objectives To determine how grain feeding impairs the deuterium-depleting functions of the anaplerotic mitochondrial matrix during milk and meat production. Methods Based on published...
Preprint
Full-text available
Real-time feedback-driven single-particle tracking (RT-FD-SPT) is a class of techniques in the field of single-particle tracking that uses feedback control to keep a particle of interest in a detection volume. These methods provide high spatiotemporal resolution on particle dynamics and allow for concurrent spectroscopic measurements. This review a...
Conference Paper
Full-text available
The international electromagnetic field (EMF) project of the World Health Organization (WHO) is a collaborative effort of the WHO teams for Environment, Climate Change and Health (ECCH) and Radiation and Health (ionizing and non-ionizing). The purpose of the effort is twofold. Firstly it seeks to create and house a database of legislation pertainin...
Article
In hyper‐arid soil environments, photosynthetic microorganisms are largely restricted to hypolithic (sub‐lithic) habitats: i.e., on the ventral surfaces of translucent pebbles in desert pavements. Here, we combined fluorometric, spectroscopic, biochemical and metagenomic approaches to investigate in situ the light transmission properties of quartz...
Conference Paper
The functional dynamics of photosynthetic light-harvesting pigment-protein complexes play an essential physiological role. The dynamic switching between different states – associated with different spectroscopic signatures – allows these complexes to regulate the excitation energy flow in the photosynthetic apparatus as a direct response to changin...
Conference Paper
One of the main challenges in studying single biomolecules in a native or near-native environment is their constant diffusive motion. A method capable of keeping a single biomolecule in the detection volume without disturbing its surrounding environment is real-time single-particle tracking (SPT). There are a number of real-time SPT methods in use,...
Article
One of the main challenges in studying single biomolecules in a native or near-native environment is their constant diffusive motion. A method capable of keeping a single biomolecule in the detection volume without disturbing its surrounding environment is real-time single-particle tracking (SPT). There are a number of real-time SPT methods in use,...
Article
Elemental doping of hematite has been widely performed to improve its mobility, electrical conductivity as well as to suppress electron–hole recombination in photoelectrochemical applications. When hematite is doped with high titanium concentrations, above 5%, pseudobrookite layers may be formed as overlayers leading to improved photocurrent while...
Article
Full-text available
Plasmon coupling between the dipolar localized surface plasmons of a nanoegg and the longitudinal dipolar localized surface plasmons of a nearby gold nanorod is investigated within a dipolar-quasistatic limit. This was achieved by varying the core-offset of the nanoegg for different nanorod sizes at a fixed coupling distance. With respect to the pl...
Article
Hematite nanoparticles were synthesized using chemical spray pyrolysis. Precursor concentrations of 30, 40, and 50 mM, deposition temperatures of 250, 340, and 400°C were used. X-ray diffraction measurements confirmed the purity of hematite with no other phases of iron oxide. The (104) and (110) diffraction peaks associated with corundum structure...
Article
We investigate the impact of the dipole-active modes formed via the mode-mixing of the dipole mode with higher-order surface plasmon modes of a nanoegg on the radiative decay rate and quantum yield of an excited molecule near the nanoegg. The Purcell factor, rate of power dissipation by the emitter, and antenna efficiency of the nanoegg, as well as...
Article
We present a derivation of a formula for Zernike-Gauss circle coefficients expressed in terms of Zernike circle coefficients for a circular Gaussian pupil by revisiting a method in which theorthonormal Zernike-Gauss circle polynomials are not derived first. This is achieved by utilizing a new result, based on the extended Nijboer-Zernike diffractio...
Article
Phycobilisomes (PBs) absorb light and supply downstream photosynthetic processes with excitation energy in many cyanobacteria and algae. In response to a sudden increase in light intensity, excess excitation energy is photoprotectively dissipated in PBs by means of the orange carotenoid protein (OCP)-related mechanism or via a light-activated intri...
Preprint
We investigate the impact of the dipole-active modes formed via the mode-mixing of the dipole mode with higher-order surface plasmon modes of a nanoegg on the radiative decay rate and quantum yield of an excited molecule near the nanoegg. The Purcell factor, rate of power dissipation by the emitter, antenna efficiency of the nanoegg, as well as qua...
Article
We report on the properties of hematite thin films prepared by spray pyrolysis on fluorine-doped tin oxide (FTO)-coated glass substrates and investigated the effect of the spray volume, tetraethoxysilicate treatment of the hematite, and post-annealing at 500 °C for 2 h with 10 °C/min ramping. Raman spectroscopy confirmed the characteristic Raman sp...
Article
Full-text available
We derive and present systematic relationships between the analytical formulas for calculation of the localized surface plasmon resonances (LSPR) of some plasmonic nanostructures which we have categorized as simple. These relationships, including some new formulas, are summarized in a tree diagram which highlights the core-shell plasmons as the gen...
Article
Nanostructured hematite films were synthesized using spray pyrolysis and chemical bath deposition. X-ray diffraction measurements revealed sharp diffraction peaks of (012), (104) and (110), describing corundum hexagonal structure of hematite. Raman spectroscopy confirmed polycrystalline hematite symmetry with two Eg and five A1g vibrational phonon...
Poster
Full-text available
Introduction Plasmon-enhanced fluorescence (PEF) is the combined effect of excitation rate enhancement due to plasmon excitation of the localized surface plasmons of a metal nanoparticle (MNP), and an increase in the radiative decay rate of an emitter placed near the MNP [3]. The latter is known as Purcell effect [3, 6]. In reality, PEF does not al...
Article
Plasmonic coupling of metallic nanoparticles and adjacent pigments can dramatically increase the brightness of the pigments due to the enhanced local electric field. Here, we demonstrate that the fluorescence brightness of a single plant light-harvesting complex (LHCII) can be significantly enhanced when coupled to a gold nanorod (AuNR). The AuNRs...
Article
Hematite, a common type of iron oxide, is a promising material for solar technologies, due to its small bandgap that allows for solar radiation absorption in the visible region, low toxicity in aqueous solutions, easy synthesis and natural abundance. However, fast electron–hole recombination has been hampering full applicability of hematite in sola...
Preprint
Full-text available
We derive and present systematic relationships between the analytical formulas for calculation of the localized surface plasmon resonances (LSPR) of some plasmonic nano-structures which we have categorized as simple. These relationships, including some new formulas, are summarized in a tree diagram which highlights the core-shell plasmons as the ge...
Preprint
Plasmonic coupling of metallic nanoparticles and adjacent pigments can dramatically increase the brightness of the pigments due to the enhanced local electric field. Here, we demonstrate that the fluorescence brightness of a single plant light-harvesting complex (LHCII) can be significantly enhanced when coupled to single gold nanorods (AuNRs). The...
Article
Full-text available
The main light-harvesting pigment-protein complex of cyanobacteria and certain algae is the phycobilisome, which harvests sunlight and regulates the flow of absorbed energy to provide the photochemical reaction centres with a constant energy throughput. At least two light-driven mechanisms of excited energy quenching in phycobilisomes have been ide...
Article
Full-text available
Biological systems are dynamical, constantly exchanging energy and matter with the environment in order to maintain the non-equilibrium state synonymous with living. Developments in observational techniques have allowed us to study biological dynamics on increasingly small scales. Such studies have revealed evidence of quantum mechanical effects, w...
Article
Transient absorption spectroscopy has been applied to investigate the energy dissipation mechanisms in the nonameric fucoxanthin-chlorophyll-a,c-binding protein FCPb of the centric diatom Cyclotella meneghiniana. FCPb complexes in their unquenched state were compared with those in two types of quenching environments, namely aggregation-induced quen...
Article
Full-text available
The concept of orthonormal vector circle polynomials is revisited by deriving a set from the Cartesian gradient of Zernike polynomials in a unit circle using a matrix-based approach. The heart of this model is a closed-form matrix equation of the gradient of Zernike circle polynomials expressed as a linear combination of lower-order Zernike circle...
Article
Photosynthetic organisms have found various smart ways to cope with unexpected changes in light conditions. In many cyanobacteria, the lethal effects of a sudden increase in light intensity are mitigated mainly by the interaction between phycobilisomes (PBs) and the Orange Carotenoid Protein (OCP). The latter senses high light intensities by means...
Article
Full-text available
The far-field divergence of a light beam propagating through a first order optical system is presented as a square root of the sum of the squares of the local divergence and the curvature divergence. The local divergence is defined as the ratio of the beam parameter product to the beam width whilst the curvature divergence is a ratio of the space-a...
Article
Full-text available
Solar energy captured by pigments embedded in light-harvesting complexes can be either transferred to neighboring pigments, dissipated or emitted as fluorescence. Only when it reaches a reaction center the excitation energy is stabilized in the form of a charge separation and converted into chemical energy. Well directed and regulated energy transf...
Article
Full-text available
The conversion of solar radiation to chemical energy in plants and green algae takes place in the thylakoid membrane. This amphiphilic environment hosts a complex arrangement of light-harvesting pigment-protein complexes that absorb light and transfer the excitation energy to photochemically active reaction centers. This efficient light-harvesting...
Conference Paper
Full-text available
The ultrafast transient dynamics of the main plant light-harvesting complex, LHCII, of spinach leaves were studied using transient absorption (TA) pump-probe spectroscopy. Explicitly, the excitation energy transfer (ET) processes within and amongst the protein-bound pigments (viz. chlorophylls (Chls) and carotenoids (Cars)) were investigated. These...
Article
Full-text available
Strong excitonic interactions are a key design strategy in photosynthetic light harvesting, expanding the spectral cross-section for light absorption and creating considerably faster and more robust excitation energy transfer. These molecular excitons are a direct result of exceptionally densely packed pigments in photosynthetic proteins. The main...
Article
Full-text available
It has already been established that the quaternary structure of the main light-harvesting complex (LH2) from the photosynthetic bacterium Rhodopseudomonas palustris is a nonameric 'ring' of PucAB heterodimers and under low-light culturing conditions an increased diversity of PucB synthesis occurs. In this work, single molecule fluorescence emissio...
Article
Full-text available
Photosynthesis operates at the bottom of the food chain to convert the energy of light into carbohydrates at a remarkable global rate of about 130 TW. Nonetheless, the overall photosynthetic process has a conversion efficiency of a few percent at best, significantly less than bottom-up photovoltaic cells. The primary photosynthetic steps, consistin...
Article
Full-text available
Hematite is a widely investigated material for applications in solar water oxidation due primarily to its small bandgap. However, full realization of the material continues to be hampered by fast electron-hole recombination rates among other weaknesses such as low hole mobility, short hole diffusion length and low conductivity. To address the probl...
Article
Full-text available
The concept of orthonormal polynomials is revisited by developing a Zernike-based orthonormal set for a non-circular pupil that is transmitting an aberrated, non-uniform field. We refer to this pupil as a general pupil. The process is achieved by using the matrix form of the Gram-Schmidt procedure on Zernike circle polynomials and is interpreted as...
Article
Photosystem II (PSII) is a huge pigment–protein supercomplex responsible for the primary steps of photosynthesis in green plants. Its light-harvesting antenna exhibits efficient transfer of the absorbed excitation energy to the reaction center and also contains a well-regulated protection mechanism against over-excitation in strong light conditions...
Article
Full-text available
Biology offers a boundless source of adaptation, innovation, and inspiration. A wide range of photosynthetic organisms exist that are capable of harvesting solar light in an exceptionally efficient way, using abundant and low-cost materials. These natural light-harvesting complexes consist of proteins that strongly bind a high density of chromophor...
Article
Full-text available
In light harvesting complex II (LHCII) of higher plants and green algae, carotenoids (Cars) have an important function to quench chlorophyll (Chl) triplet states and therefore avoid the production of harmful singlet oxygen. The resulting Car triplet states lead to a non-linear self-quenching mechanism called singlet–triplet (S–T) annihilation that...
Article
Full-text available
Among the ultimate goals of protein physics, the complete, experimental description of the energy paths leading to protein conformational changes remains a challenge. Single protein fluorescence spectroscopy constitutes an approach of choice for addressing protein dynamics, and, among naturally fluorescing proteins, light-harvesting (LH) proteins f...