Jeroen Lammertyn

Light penetration properties of NIR radiation in fruit with respect to non-destructive quality assessment

Abstract Some issues related to the non-destructive measurement of apple quality attributes by means of NIR reflectance spectroscopy are addressed. A comparison was made between two optical configurations, which can be used to perform NIR-spectroscopic measurements: the bifurcated and the 0°/45° optical configuration. A relationship was established between the reflectance spectra (880–1650 nm) and the soluble solids content by means of the partial least squares technique. Depending on the data pre-processing method, correlation coefficients between 79 and 91% were obtained. The results obtained with the bifurcated fibre were only marginally better than those obtained with the 0°/45° configuration. The apple skin reflectance and skin transmission properties with regard to NIR radiation were also investigated. The intensity of the light source was high enough to penetrate through the apple skin and gather information about the apple parenchyma tissue. A method was developed to calculate the light penetration depth for each wavelength in the range from 500 to 1900 nm. This method was applied to measure the light penetration depth in ‘Jonagold’ apple fruit tissue. The penetration depth is wavelength dependent: up to 4 mm in the 700–900 nm range and between 2 and 3 mm in the 900–1900 nm range.

Fiber optic SPR biosensing of DNA hybridization and DNA–protein interactions

In this paper we present a fiber optic surface plasmon resonance (SPR) sensor as a reusable, cost-effective and label free biosensor for measuring DNA hybridization and DNA-protein interactions. This is the first paper that combines the concept of a fiber-based SPR system with DNA aptamer bioreceptors. The fibers were sputtered with a 50nm gold layer which was then covered with a protein repulsive self-assembled monolayer of mixed polyethylene glycol (PEG). Streptavidin was attached to the PEGs carboxyl groups to serve as a versatile binding element for biotinylated ssDNA. The ssDNA coated SPR fibers were first evaluated as a nucleic acid biosensor through a DNA-DNA hybridization assay for a random 37-mer ssDNA. This single stranded DNA showed a 15 nucleotides overlap with the receptor ssDNA on the SPR fiber. A linear calibration curve was observed in 0.5-5 microM range. A negative control test did not reveal any significant non-specific binding, and the biosensor was easily regenerated. In a second assay the fiber optic SPR biosensor was functionalized with ssDNA aptamers against human immunoglobulin E. Limits of detection (2nM) and quantification (6nM) in the low nanomolar range were observed. The presented biosensor was not only useful for DNA and protein quantification purposes, but also to reveal the binding kinetics occurring at the sensor surface. The dissociation constant between aptamer and hIgE was equal to 30.9+/-2.9nM. The observed kinetics fully comply with most data from the literature and were also confirmed by own control measurements.

Prediction of the optimal picking date of different apple cultivars by means of VIS/NIR-spectroscopy

Abstract The use of visible/near infrared (VIS/NIR) spectroscopy was evaluated to determine the internal quality and the optimal harvest dates of apples non-destructively. Calibration models were constructed with data from eight cultivars, three orchards and 2 years, in order to make the models as robust as possible for future use. The prediction of the maturity, defined as the number of days before commercial harvest, was reasonably accurate. The most robust model predicted the maturity with a validation correlation of 0.90 (SEP=7.4 days). The prediction of maturity, according to the Streif index, showed a validation correlation of 0.84 (SEP=0.18 kg/% brix×starch index) for one orchard. Maturity was orchard-dependent, however, and as a consequence, a combined prediction equation was not accurate. Individual quality characteristics (soluble solids, Streif index, acidity and firmness) were well predicted. The calibration model for soluble solids content resulted in a validation correlation of 0.84 (SEP=0.73% brix) for the results over 2 years from one orchard, but like the Streif index, was orchard-dependent and appeared to account largely for the orchard dependence of the latter. Acidity and firmness were predicted with a validation correlation of 0.80 and 0.78 and SEPs of 2.07 ml NaOH and 1.13 kg for, respectively, two and three orchards over the 2 years.

Electronic nose as a non-destructive tool to evaluate the optimal harvest date of apples

Abstract An electronic nose (E-nose) has been evaluated for use as a tool to predict the optimal harvest date of apples ( Malus domestica Borkh.). The volatiles of ‘Jonagold’ and ‘Braeburn’ apples were assessed during the preclimacteric stage for two consecutive harvest years by means of an E-nose. A principal component data analysis indicated the presence of both a year and cultivar effect. Partial least square (PLS) models were constructed based on data of both harvest years. The cultivar effect made it difficult to build accurate and robust models for the two cultivars together. As a consequence, calibration models were constructed based on data of 2 years, but for each cultivar separately. The prediction of maturity, according to the Streif Index, showed a cross-validation correlation of 0.89 and 0.92 for ‘Jonagold’ and ‘Braeburn’ fruit, respectively. The calibration models for the prediction of the maturity, defined as the number of days before commercial harvest had a validation correlation of 0.91 for ‘Jonagold’ and 0.84 for ‘Braeburn’ fruit. Individual quality characteristics (soluble solids, acidity, starch and firmness) were predicted reasonably well. The calibration model for soluble solids content resulted in a consistent validation correlation over the results over 2 years (0.76 and 0.77). The starch and firmness were predicted with a validation correlation between 0.72 and 0.80. The prediction of the total acidity was poor (validation correlation of 0.66 and 0.69). It was also demonstrated that the type of validation influences the model prediction performance. Care should be taken when interpreting and using the models to predict the optimal harvest date for other years and cultivars.

Fast and accurate peanut allergen detection with nanobead enhanced optical fiber SPR biosensor

This paper is the first report of a fiber optic SPR biosensor with nanobead signal enhancement. We evaluated the system with a bioassay for the fast and accurate detection of peanut allergens in complex food matrices. Three approaches of an immunoassay to detect Ara h1 peanut allergens in chocolate candy bars were compared; a label-free assay, a secondary antibody sandwich assay and a nanobead enhanced assay. Although label-free detection is the most convenient, our results illustrate that functionalized nanobeads can offer a refined solution to improve the fiber SPR detection limit. By applying magnetite nanoparticles as a secondary label, the detection limit of the SPR bioassay for Ara h1 was improved by two orders of magnitude from 9 to 0.09 μg/mL. The super paramagnetic character of the nanoparticles ensured easy handling. The SPR fibers could be regenerated easily and one fiber could be reused for up to 35 times without loss of sensitivity. The results were benchmarked against a commercially available polyclonal ELISA kit. An excellent correlation was found between the Ara h1 concentrations obtained with the ELISA and the concentrations measured with the SPR fiber assay. In addition, with the SPR fiber we could measure the samples twice as fast as compared to the fastest ELISA protocol. Since the dipstick fiber has no need for microchannels that can become clogged, time consuming rinsing step could be avoided. The linear dynamic range of the presented sensor was between 0.1 and 2 μg/mL, which is considerably larger than the ELISA benchmark.

Selection of aptamers against Ara h 1 protein for FO-SPR biosensing of peanut allergens in food matrices

The rising prevalence to food allergies in the past two decades, together with the fact that the only existing therapy is avoidance of allergen-containing food next to the implementation of anti-allergic drugs, urges the need for improved performance of current assays to detect potential allergens in food products. Therein, the focus has been on aptamer-based biosensors in recent years. In this paper we report for the first time the selection of aptamers against one of the most important peanut allergens, Ara h 1. Several Ara h1 DNA aptamers were selected after eight selection rounds using capillary electrophoresis (CE)-SELEX. The selected aptamers specifically recognized Ara h 1 and did not significantly bind with other proteins, including another peanut allergen Ara h 2. The dissociation constant of a best performing aptamer was in the nanomolar range as determined independently by three different approaches, which are surface plasmon resonance, fluorescence anisotropy, and capillary electrophoresis (353 ± 82 nM, 419 ± 63 nM, and 450 ± 60 nM, respectively). Furthermore, the selected aptamer was used for bioassay development on a home-built fiber optic surface plasmon resonance (FO-SPR) biosensor platform for detecting Ara h 1 protein in both buffer and food matrix samples demonstrating its real potential for the development of novel, more accurate aptamer-based biosensors. In conclusion, the reported aptamer holds a great potential for the detection of Ara h 1 in both the medical field and the food sector due to its high affinity and specificity for the target protein.

A versatile electrowetting-based digital microfluidic platform for quantitative homogeneous and heterogeneous bio-assays

Electrowetting-on-dielectric (EWOD) lab-on-a-chip systems have already proven their potential within a broad range of bio-assays. Nevertheless, research on the analytical performance of those systems is limited, yet crucial for a further breakthrough in the diagnostic field. Therefore, this paper presents the intrinsic possibilities of an EWOD lab-on-a-chip as a versatile platform for homogeneous and heterogeneous bio-assays with high analytical performance. Both droplet dispensing and splitting cause variations in droplet size, thereby directly influencing the assays performance. The extent to which they influence the performance is assessed by a theoretical sensitivity analysis, which allows the definition of a basic framework for the reduction of droplet size variability. Taking advantage of the optimized droplet manipulations, both homogeneous and heterogeneous bio-assays are implemented in the EWOD lab-on-a-chip to demonstrate the analytical capabilities and versatility of the device. A fully on-chip enzymatic assay is realized with high analytical performance. It demonstrates the promising capabilities of an EWOD lab-on-a-chip in food-related and medical applications, such as nutritional and blood analyses. Further, a magnetic bio-assay for IgE detection using superparamagnetic nanoparticles is presented whereby the nanoparticles are used as solid carriers during the bio-assay. Crucial elements are the precise manipulation of the superparamagnetic nanoparticles with respect to dispensing and separation. Although the principle of using nano-carriers is demonstrated for protein detection, it can be easily extended to a broader range of bio-related applications like DNA sensing. In heterogeneous bio-assays the chip surface is actively involved during the execution of the bio-assay. Through immobilization of specific biological compounds like DNA, proteins and cells a reactive chip surface is realized, which enhances the bio-assay performance. To demonstrate this potential, on-chip adhesion islands are fabricated to immobilize MCF-7 human breast cancer cells. Viability studies are performed to assess the functionalization efficiency.

Digital Microfluidic High‐Throughput Printing of Single Metal‐Organic Framework Crystals

The first microfluidic method for accurately depositing monodisperse single MOF crystals is presented, enabling unprecedented high-throughput, yet flexible single-crystal printing. Individual droplets of MOF precursor solutions are actuated over a matrix of hydrophilic-in-hydrophobic micropatterns for the controlled generation of femtoliter droplets. As such, thousands of monodisperse single MOF crystals are printed per second in a desired pattern, without the use of impractically expensive equipment.

Changes in chemical wax composition of three different apple (Malus domestica Borkh.) cultivars during storage

Abstract The effects of year, picking date and storage conditions on the chemical composition of the wax layer of three apple cultivars (‘Jonagold’, ‘Jonagored’ and ‘Elstar’) were investigated by means of GCMS and multivariate statistical techniques. Wax of apples with different surface characteristics also differed in chemical composition. Controlled atmosphere (CA) storage and subsequent shelf life affected wax properties and caused changes in the chemical composition, especially during shelf life. The changes in wax composition of ‘Elstar’, however, were smaller than those in ‘Jonagold’ and ‘Jonagored’, possibly associated with lower diffusion resistance and more limited structural changes of ‘Elstar’ wax. Longer CA storage periods accelerated the changes in wax composition during subsequent shelf life. The components responsible for the changes were mainly the alkane and ester fractions. The secondary alcohol nonacosan-10-ol was particularly important in explaining the changes in wax composition of ‘Jonagold’ during shelf life and its presence could be linked with greater development of greasiness.

Nanocrystalline diamond impedimetric aptasensor for the label-free detection of human IgE

Like antibodies, aptamers are highly valuable as bioreceptor molecules for protein biomarkers because of their excellent selectivity, specificity and stability. The integration of aptamers with semiconducting materials offers great potential for the development of reliable aptasensors. In this paper we present an aptamer-based impedimetric biosensor using a nanocrystalline diamond (NCD) film as a working electrode for the direct and label-free detection of human immunoglobulin E (IgE). Amino (NH(2))-terminated IgE aptamers were covalently attached to carboxyl (COOH)-modified NCD surfaces using carbodiimide chemistry. Electrochemical impedance spectroscopy (EIS) was applied to measure the changes in interfacial electrical properties that arise when the aptamer-functionalized diamond surface was exposed to IgE solutions. During incubation, the formation of aptamer-IgE complexes caused a significant change in the capacitance of the double-layer, in good correspondence with the IgE concentration. The linear dynamic range of IgE detection was from 0.03 μg/mL to 42.8 μg/mL. The detection limit of the aptasensor reached physiologically relevant concentrations (0.03 μg/mL). The NCD-based aptasensor was demonstrated to be highly selective even in the presence of a large excess of IgG. In addition, the aptasensor provided reproducible signals during six regeneration cycles. The impedimetric aptasensor was successfully tested on human serum samples, which opens up the potential of using EIS for direct and label-free detection of IgE levels in blood serum.