Browsing by Author "Higson, Seamus P. J."
Now showing 1 - 20 of 36
Results Per Page
Sort Options
Item Open Access Carrier systems and biosensors for biomedical applications.(2007-10-31T00:00:00Z) Davis, Frank; Higson, Seamus P. J.This chapter addresses both carrier systems and biosensors which are often applied directly to tissues, either as skin patches, implanted or ingested by a variety of routes. It follows that there is a common theme between these applications and many of those discussed elsewhere within this book. Any device, scaffold or implant within the body must usually display extreme biocompatibility if it is not to cause harm to the patient. The techniques of tailoring surfaces to ensure no adverse reactions are a common theme running throughout this work on tissue engineering.Item Open Access Construction and interrogation of enzyme microarrays using scanning electrochemical microscopy - optimisation of adsorption and determination of enzymatic activity.(Royal Society of Chemistry, 2011-12-21T00:00:00Z) Roberts, William St John; Davis, Frank; Collyer, Stuart D.; Higson, Seamus P. J.Scanning electrochemical microscopy (SECM) has been used to image and study the catalytic activity of horseradish peroxidase (HRP) immobilised in a patterned fashion onto glass slides. Microarrays of HRP islands could be deposited on amino-modified glass slides using glutaraldehyde crosslinking combined with the SECM being used as a micro-deposition device. The enzymatic activity of the immobilised enzyme on the surface was in the presence of its substrate observed to give rise to substantial positive feedback between the slide and the SECM microelectrode tip. Conversely when either blank slides - or slides coated with HRP which had been subsequently thermally denatured were utilised, these showed negative feedback effects. Various conditions such as enzyme concentration, incubation time and substrate concentration were systematically varied to optimise sensitivity. Regular arrays of HRP could be assembled and when imaged, displayed lower limits of detection of 1.2 × 10(-12) mol ml(-1) of benzoquinone.Item Open Access Current trends in explosive detection techniques(Elsevier Science B.V., Amsterdam., 2012-01-15T00:00:00Z) Caygill, J. S.; Davis, Frank; Higson, Seamus P. J.The detection of explosives and explosive-related compounds has become a heightened priority in recent years for homeland security and counter-terrorism applications. There has been a huge increase in research within this area- through both the development of new, innovative detection approaches and the improvement of existing techniques. Developments for miniaturisation, portability, field-ruggedisation and improvements in stand-off distances, selectivity and sensitivity have been necessary to develop and improve techniques. This review provides a consolidation of information relating to recent advances in explosive detection techniques without being limited to one specific research area or explosive type. The focus of this review will be towards advances in the last 5 years, with the reader being referred to earlier reviews where appropriate.Item Open Access Detection of volatile organic compounds (VOCs) using an optical fibre long period grating with a calixarene anchored mesoporous thin film(SPIE, 2013-05-06) Korposh, Sergiy; Davis, Frank; James, Stephen W.; Wang, T.; Lee, Seung-Woo; Higson, Seamus P. J.; Tatam, Ralph P.A long period grating (LPG) modified with a mesoporous film infused with a functional compound, calix[4]arene, was employed for the detection of volatile organic compounds (VOCs). The mesoporous film consisted of an inorganic part, of SiO2 nanoparticles (NPs) along with an organic moiety of poly(allylamine hydrochloride) polycation PAH, which was finally infused with functional compound, p-sulphanatocalix[4]arene (CA[4]). The LPG sensor was designed to operate at the phase matching turning point to provide the highest sensitivity. The sensing mechanism is based on the measurement of the refractive index (RI) change induced by the complexion of the VOCs with calix[4]arene (CA). The LPG modified with 5 cycles of (SiO2 NPs/PAH)5PAA responded to exposure to chloroform and benzene vapours. The sensitivity to humidity as an interfering parameter was also investigated.Item Open Access Development of a flexible biosensor for the monitoring of lactate in human sweat for its medical use in pressure ischemia(Cranfield University, 2014-11) Tur García, Eva; Higson, Seamus P. J.Pressure ischemia is a medical condition characterised by the necrosis of the skin and underlying tissues in body areas exposed to prolonged pressure. This condition leads to the development of bedsores and affects 9% of hospitalised patients, costing the NHS between £1.4 and £2.1 billion per year. The severity of pressure ischemia has been linked to the concentration of sweat lactate, a product of sweat gland metabolism under anaerobic conditions, such as hypoxia. Normal levels of lactate in human sweat are 20±7 mM, but under ischemic conditions these can rise up to approximately 70 mM. This project presents the development of a novel flexible electrochemical enzyme-based biosensor for the continuous and non-invasive monitoring of sweat lactate with the potential for becoming a body-worn device for the early detection of pressure ischemia onset. The core of the recognition system is a flexible laminate, comprising two highly porous polycarbonate membranes, which provide support for the lactate oxidase enzyme, immobilised via covalent cross-linking. Oxidation of lactate produces H2O2, which is subsequently determined electrochemically. The transducer comprises a two-electrode system on a single flexible polycarbonate membrane, sputter-coated with gold (CE/RE) and platinum (WE) to render it conductive. The developed design has been improved through investigation into different factors regarding the immobilisation method of the enzyme in the laminate and the lowering of interferences from oxidising compounds present in sweat. The sensing system exhibits lactate selectivity at physiologically relevant concentrations in sweat for pressure ischemia (0–70 mM), with good reproducibility (7.2–12.2% RSD) for a hand-manufactured device. The reliability of the sensor’s performance and the capability to detect lactate fluctuations on human sweat samples has been demonstrated. The sensing system showed excellent operational and mechanical stability. The application of Nafion® on the WE lowered interferences from ascorbic acid and uric acid by 96.7 and 81.7% respectively. These results show promise towards the further development of a body-‐worn monitoring device for determining lactate levels in undiluted human sweat samples in a reproducible, fast and accurate manner.Item Open Access Development of impedimetric immunosensors for the detection of a range of antigens of biological or biomedical significance(Cranfield University, 2008) Garifallou, Goulielmos-Zois; Higson, Seamus P. J.This PhD project was funded by the European Union Framework 6 ELISHA programme as part of the ELISHA programme. The aim of the research was focused towards the development of point-of-care, simple, cost-efficient and reliable impedimetric immunosensors for the rapid detection of important antigens such as ciprofloxacin and digoxin. Through the cooperation of the 9 involved partners a number of protocols have been developed for sensor fabrication and sample testing that allow both rapid and reliable detection of a range of antigens. This work describes in depth, the use of polymers and cyclic voltammetry for electrode surface modification, the use of the avidin-biotin system for antibody immobilisation and finally the use of Electrochemical Impedance Spectroscopy for antigen detection. We report here the successful development of electrochemical impedimetric carbon based immunosensors for the detection of free-form and chelated ciprofloxacin (both in laboratory buffer and milk), digoxin and green fluorescent protein. It was observed during this work that unavailability of sufficient quantities of the monoclonal antibodies could lead to early sensor saturation and hence a less extended antigen detection range, while very low quantities of immobilised antibodies could also give rise to erroneous results. The immunosensors towards ciprofloxacin detected the respective antigen when this was present between 1 ng ml-1 and 10 μg ml-1 in PBS buffer and 0.1 ng ml-1 to 10 μg ml-1 when the antigen was added to milk samples. The developed digoxin immunosensors could detect digoxin between the concentrations of 0.1 ng ml-1 and 10 μg ml-1. Lower detection limits where observed for the sensors targeting GFP which could detect their respective antigen at concentrations as low as 100 pg ml-1. The tested concentration range of the latter sensors was extended up to 100 ng ml-1.Item Open Access Development of Polyaniline as a Sensor for Food Quality and Spoilage Detection(Cranfield University, 2009-12) Hobday, Duncan Stuart; Higson, Seamus P. J.; Kagan, Michael; Allen, Tristan; Isbitsky, Reuben; Mena, CarlosThis thesis describes the research that has been completed for the application of polyaniline as a food quality indicator. It has been reported by WRAP (Waste and Resources Action Programme) that in the UK alone, a third of all purchased food items are thrown away regardless of the quality or condition. It has also been reported by DEFRA (Department for Environment Food and Rural Affairs) that the food manufacturing and processing industry is one of the UK’s largest producers of land filled waste. At present, the available technology for food freshness determination is largely based on use-by dates which are often recognised as unreliable - or qualitative time temperature indicators (TTIs); which can be costly and do not give an actual measurement of bacterial activity. It is anticipated that the technology produced from this research will give a viable and low cost solution to help minimize preventable food waste from consumers - as well as improving food industry process efficiency, especially in the field of food supply chain management. The sensors being developed employ a conducting polymer film as a sensor which reacts with volatiles evolving from selected food products (salmon and herring). As food biochemically degrades, the concentrations and volumes of these gases change, and this has been studied by analytical techniques such as gas chromatography and SIFT-MS. Food spoilage has also been followed by the growth and identification of specific spoilage bacteria. The sensor exhibits a number of quantifiable physical changes when exposed to differing volatile mixtures produced by the food stuffs. These physical properties include colour and conductivity changes which are distinctive and easily measurable. Correlations have been shown between increases in microbial activity and the change in conductivity of the films. These sensors will be able to inform consumers more reliably when the food is safe to consume as well as providing the food industry with more information on traceability and stock conditions of fresh meat and fish. In the context of the catering industry, these sensors will also aid in the decreasing the number of reported cases of food poisoning by observing - in real-time - the condition and safety of food.Item Open Access Editorial, Seminars in Cell & Developmental Biology(Elsevier Science B.V., Amsterdam, 2009-02-01T00:00:00Z) Davis, Frank; Higson, Seamus P. J.It is a pleasure to introduce this special edition of Cell and Development Biology dedicated to the field and application of Biosensors. This edition comprises seven reviews covering the most active research areas where we believe some of the most prominent advances in the field are likely to emerge in the near to medium term. In line with scope of this journal, some emphasis is given towards techniques applicable to Cell Biology.Item Open Access Electrochemical detection of TNT at cobalt phthalocyanine mediated screen-printed electrodes and application to detection of airborne vapours(Wiley-Blackwell, 2013-10-11) Caygill, J. S.; Collyer, Stuart D.; Holmes, Joanne L.; Davis, Frank; Higson, Seamus P. J.We describe the use of cobalt phthalocyanine as a mediator to improve the sensitivity for the electrochemical detection of TNT. Commercial screen-printed electrodes containing cobalt phthalocyanine were employed for determination of TNT. Improved sensitivities compared to screen-printed carbon electrodes without phthalocyanine were observed, current response for cyclic voltammetric measurements at modified electrodes being at least double that of unmodified electrodes. A synergistic effect between oxygen and TNT reduction was also observed. Correlation between TNT concentrations and sensor output was observed between 0–200 µM TNT. Initial proof-of-concept experiments combining electrochemical determinations, with the use of an air-sampling cyclone, are also reported.Item Open Access The electrochemistry of the ferri/ferrocyanide couple at a calix [4]resorcinarenetetrathiol-modified gold electrode as a study of novel electrode modifying coatings for use within electro-analytical sensors(Elsevier Science B.V., Amsterdam., 2003-06-05T00:00:00Z) Collyer, Stuart D.; Davis, Frank; Lucke, Andrew; Stirling, Charles J. M.; Higson, Seamus P. J.The electrochemistry of the ferri/ferrocyanide redox couple has been studied at Au electrodes modified with calix[4]resorcinarenetetrathiol. Cyclic voltammetry in Fe(CN)63- solutions yields three separate pairs of faradaic peaks. Evidence is given for these redox couples corresponding to the reduction of Fe(CN)63- and the subsequent re-oxidation of Fe(CN)64- in three differing steric arrangements. One pair of peaks suggest that when the Fe(CN)63- ion resides within the calix [4]resorcinarene bowl, electron transport is facilitated by the calix [4]resorcinarene acting as a charge transfer mediator; in this arrangement the activation energy is found to be lowered by ~24kJmol-1. Another pair of peaks is thought to correspond to the reduction of Fe(CN)63- as it approaches the Au electrode by packing itself in-between adjacent calix[4]resorcinarene molecules. The third pair of redox peaks is attributed to the reduction and subsequent re- oxidation of Fe(CN)63-/Fe(CN)64- when the ion resides above a saturated calix [4]resorcinarene coating; in this case the activation energy was raised by ~45kJmol-1. FTIR spectroscopy of calix[4]resorcinarene-coated Au electrodes and calix[4]resorcinarene-coated Au electrodes exposed to Fe(CN)63- lends further support to this argument, by demonstrating that the Fe(CN)63- ion resides within at least two and possibly three differing environments. Calix[4]resorcinarene modified electrodes previously exposed to ferricyanide lose the calix [4]resorcinarene coating together with a surface layer of gold when subsequently scanned in a phosphate buffer. It therefore appears that the calix [4]resorcinarene/Fe(CN)63- association is stronger than the Au binding to the underlying glass material.Item Open Access Electrochromic effects from a simple commercial polymer membrane.(Elsevier Science B.V., Amsterdam., 2007-08-01T00:00:00Z) Davis, Frank; Law, Karen A.; Bridge, Kerry; Higson, Seamus P. J.A simple commercial polyester polymer membrane has been found to exhibit an intense electrochromic effect. Most polymers which undergo electrochromic effects contain either transition metals or extensive conjugated systems. We have found that a simple commercial polyester membrane when coated with gold and polarised to −4 V (versus Ag) in aprotic organic solvents displays an electrochromic colour change from a colourless to an intense red statItem Open Access Fibre-optic sensors with molecular coatings(Cranfield University, 2012-12) Partridge, Matthew; James, Stephen W.; Tatam, Ralph P.; Higson, Seamus P. J.The intrinsic stability of fibre optic based sensing systems offer a platform that is suited to hazardous waste detection in a wide range of environments. Over the last few years Cranfield University has been working on the development of chemical sensors using optical fibres in combination with a group of chemical recognition molecules called calixarenes. Calixarenes semi-selectively with a range of solvents of interest makes them useful for chemical detection systems. This work has primarily been focused on the use of calixarenes in sensing benzene and other hazardous solvents. However, this approach could potentially be expanded for use in a wide range of chemical and even biological recognition systems. The initial aim of this project was to build on the previous work in fibre optic sensing at Cranfield and explore approaches to improve and extend the performance of the sensor system. The project first focused on improving the techniques used in the Langmuir-Blodgett (LB) deposition of calixarenes. Initial studies in this area highlighted one critical experimental error associated with the use of dry Wilhelmy plates to monitor the surface pressure of the Langmuir film. Dry filter paper plates take up to 2 hours to give stable data, with a drift of up to 10% in the measured surface pressure. It is shown that this problem can be avoided by using pre-soaked plates. To provide an alternative to the Wilhelmy plate surface pressure senor, an optical fibre surface pressure sensor was developed, measuring changes in the meniscus forming properties of a liquid. The sensor consists of a tapered single mode silica fibre, mounted with a small curvature and positioned with the tapered region of the fibre immersed in the water. The performance of the fibre optic sensor is comparable with that of the conventional Wilhelmy plate surface pressure sensor showing linearity of greater than 0.9. Following the analysis of the experimental systems used in the construction of the sensors, the project then focused on the chemistry of the materials and their suitability for LB coating. A variety of these materials were spread as Langmuir monolayers and their behavior upon compression measured. Long chain-substituted resorcinarenes gave more stable monolayers than their short chain analogues. The incorporation of long chain surfactants led to large increases in surface area, demonstrating that both resorcinarenes and surfactants are located at the water surface, except for one system where a bilayer structure is potentially formed. Further work on the behavior of the materials involved the alteration of the dipole-dipole interaction of the monolayer materials with the subphase. The modification of this interaction through the introduction of dipole altering additives, including alcohols and hydrogen peroxide, to the aqueous subphase was investigated. The resulting isotherms of the materials showed a reduction in the surface pressure and area per molecule required in order for the monolayer to reach its point of collapse. This ability to shift the point of collapse has application in the optimisation of Langmuir-Blodgett coating of surfaces. Within this project the sensing properties of a fibre sensor were also modelled extensively in order to determine the theoretical sensing limits of a fibre optic vapour sensor. The model showed that the sensing goals of 1ppm originally envisaged for this project were unobtainable due to the low number of gas molecules interacting with the sensor. However, this led to the proposal of a new application of the system in sensing contaminants in water, where the same limitations would not apply. The results for the sensor system tested in water show how significantly more sensitive the system is to toluene contamination in water than it is to toluene vapour. These results demonstrate the utility of the developed system for many pollutant-sensing applications, include crude oil detection.Item Open Access Flexible Ultrathin PolyDVB/EVB Composite Membranes for the Optimization of a Lactate Sensor.(John Wiley & Sons, Ltd, 2007-01-01T00:00:00Z) Bridge, Kerry; Davis, Frank; Collyer, Stuart D.; Higson, Seamus P. J.An ultrathin composite membrane has been developed as the outer covering barrier in a model amperometric lactate oxidase enzyme electrode. The membrane was formed by cathodic electropolymerization of divinylbenzene/ethylvinylbenzene at the surface of a gold coated polyester support membrane. Permeability coefficients were determined for O2 and lactate across membranes with a range of polymer thicknesses. Anionic interferents (such as ascorbate) were screened from the working electrode by the composite membrane. The composite enzyme electrode showed an increased working concentration range and extended linearity of responses in comparison to an uncoated enzyme electrode.Item Open Access Graphene modified electrodes for enhanced electrochemical detection(Cranfield University, 2016-01) Walch, Nicholas John; Higson, Seamus P. J.; Davis, FrankThe ability to inexpensively and reliably detect organic compounds is important across a multitude of different areas of science. Benzene ring functional groups are found in a wide variety of biological molecules, (such as amino acids, DNA nucleotide bases and blood based components). The qualification and quantification of these compounds in a sample has been achieved by techniques such as high performance liquid chromatography (HPLC), gas chromatography (GC), mass spectrometry (MS) and nuclear magnetic resonance (NMR), amongst others. These techniques, however, often require cumbersome, expensive equipment along with exhaustive sample preparation techniques and are thus not necessarily suitable for portable in-situ analysis of these compounds. This thesis details the fabrication and characterisation of graphene modified electrodes that show an increased sensitivity towards biomolecular compounds such as dopamine, amino acids, and DNA. The graphene was synthesised using a novel semi-automated method which was performed using a bespoke apparatus designed to alleviate the labour involved in synthesising graphene by the sonochemical method. The method involved pumping an aqueous solution of the surfactant into a solution of graphite in water which was under constant sonication. When used in an electrochemical system employing cyclic voltammetry the graphene modified electrodes showed not only a lower limit of detection in all cases, but also a shift in peak position which allowed for simultaneous quantification of mixtures of compounds. This could not be achieved with screen printed carbon electrodes alone as different peaks often occur at similar potentials, making it difficult or impossible to quantify these compounds individually. Slower scan rates can often give rise to separate peaks, however this adds time to the experiment which is not necessary with graphene modification. The binding interactions of novel resorcinarene molecules were also predicted by molecular modelling techniques and then confirmed using NMR binding experiments. The resorcinarene was tested against a range of different analytes and showed a degree of specificity. The interaction between the two surfactant molecules and the graphene surface was also analysed to determine whether or not the resorcinarene molecules could be adsorbed onto graphene to produce a viable, molecularly specific electrode surface.Item Open Access Labeless AC impedimetric antibody-based sensors with pg ml-1 sensitivities for point-of-care biomedical applications.(Elsevier Science B.V., Amsterdam., 2009-01-01T00:00:00Z) Barton, Andrew C.; Collyer, Stuart D.; Davis, Frank; Garifallou, Goulielmos-Zois; Tsekenis, Georgios; Tully, Elizabeth; O'Kennedy, Richard; Gibson, Tim; Millner, Paul A.; Higson, Seamus P. J.This paper describes the development and characterisation of labeless immunosensors for (a) the cardiac drug digoxin and (b) bovine serum albumin (BSA). Commercial screen-printed carbon electrodes were used as the basis for the sensors. Two methods were used to immobilise antibodies at the electrode surface. Aniline was electropolymerised onto these electrodes to form a thin planar film of conductive polyaniline; the polyaniline film was then utilised as a substrate to immobilise biotinylated anti-digoxin using a classical avidin- biotin affinity approach. As an alternative approach, poly(1,2-diaminobenzene) was electrodeposited onto the carbon electrodes and this modified surface was then sonochemically ablated to form an array of micropores. A second electropolymerisation step was then used to co-deposit conductive polyaniline along with antibodies for BSA within these pores to produce a microarray of polyaniline protrusions with diameters of several μm, containing entrapped anti- BSAItem Open Access Langmuir and LB properties of two calix[4]resorcinarenes: Interactions with various analytes(Elsevier Science B.V., Amsterdam., 2008-05-15T00:00:00Z) Sugden, Mark W.; Richardson, Tim H.; Davis, Frank; Higson, Seamus P. J.; Faul, Charl F. J.The ability of calixarene-based molecules to interact with amino acids has been the basis of many studies. The Langmuir and LB properties of two calix [4]resorcinarenes have been investigated. The properties of the layer formed at the air–water interface were studied by surface pressure–area isotherms. LB deposition onto glass substrates has shown that multilayer assemblies can be built up. The UV–vis spectra of resulting LB films have been recorded, indicating that the compounds are coloured as a result of intra-molecular charge transfer bands. The sensitivity of the surface pressure–area isotherms has been investigated in relation to the exposure to various analytes delivered from the subphase (i.e. amino acids). Furthermore, exposure of the LB films to a wide range of vapours (e.g. amines, alcohols, thiols) has led to modified UV–viItem Open Access Long period grating based toluene sensor for use with water contamination(Elsevier Science B.V., Amsterdam., 2014-11-01T00:00:00Z) Partridge, Matthew; Wong, Rebecca; James, Stephen W.; Davis, Frank; Higson, Seamus P. J.; Tatam, Ralph P.A demonstration of the use of a calix[4]resorcinarene coated optical fibre long period grating sensor for the detection of toluene in water is presented. Monitoring water quality both for domestic use and around industrial sites is critical to the preservation of clean water provision. Here we show that, by using a fibre optic based sensor system, water quality monitoring can be carried out without the requirement for water sampling or pre-concentration. The results presented demonstrate that this proof-of-concept sensor is capable of sensing ∼100ppm concentrations of toluene with semi-selectivity and low (<10ppm) variation.Item Open Access Modifying monolayer behaviour by incorporating subphase additives and improving Langmuir–Blodgett thin film deposition on optical fibres(Elsevier, 2014-01-17) Partridge, Matthew; Wong, Rebecca; Collins, Mike; James, Stephen W.; Davis, Frank; Tatam, Ralph P.; Higson, Seamus P. J.Experiments showing the possibility of modifying the behaviour of calix[4]resorcinarene monolayers at the air–water interface and optimising the deposition of multilayer coatings onto optical fibres are presented. The nature of the subphase is fundamental to the behaviour of monolayers and their utility in coating and sensing applications. Here we show initial studies exploring the modification of the calix[4]resorcinarene monolayer–water interaction through the introduction of dipole altering alcohol additives to the aqueous subphase. We explored the effect of this modification for three small alcohols. The resulting isotherms of the materials showed a reduction in the surface pressure and area per molecule required in order for the monolayer to reach its point of collapse. Incorporation of alcohols shifted the point of collapse, leading to the application of ethanol being successful in improving the transfer of material via Langmuir–Blodgett coating onto optical fibres at lower pressures. This method may prove useful in allowing greater control over future sensor surface coatings.Item Open Access A new application of scanning electrochemical microscopy for the label-free interrogation of antibody-antigen interactions.(Elsevier Science B.V., Amsterdam., 2011-03-18T00:00:00Z) Holmes, Joanne L.; Davis, Frank; Collyer, Stuart D.; Higson, Seamus P. J.Within this work we present a 'proof of principle' study for the use of scanning electrochemical microscopy (SECM) to detect and image biomolecular interactions in a label-free assay as a potential alternative to current fluorescence techniques. Screen-printed carbon electrodes were used as the substrate for the deposition of a dotted array, where the dots consist of biotinylated polyethyleneimine. These were then further derivatised, first with neutravidin and then with a biotinylated antibody to the protein neuron specific enolase (NSE). SECM using a ferrocene carboxylic acid mediator showed clear differences between the array and the surrounding unmodified carbon. Imaging of the arrays before and following exposure to various concentrations of the antigen showed clear evidence for specific binding of the NSE antigen to the antibody derivatised dots. Non-specific binding was quantified. Control experiments with other proteins showed only non-specific binding across the whole of the substrate, thereby confirming that specific binding does occur between the antibody and antigen at the surface of the dots. Binding of the antigen was accompanied by a measured increase in current response, which may be explained in terms of protein electrostatic interaction and hydrophobic interactions to the mediator, thereby increasing the localised mediator flux. A calibration curve was obtained between 500 fg mL(-1) to 200 pg mL(-1) NSE which demonstrated a logarithmic relationship between the current change upon binding and antigen concentration without the need for any labelling of the substrate.Item Open Access Optical and AFM study of electrostatically assembled films of CdS and ZnS colloid nanoparticles.(Elsevier Science B.V., Amsterdam., 2008-05-30T00:00:00Z) Suryajaya, S.; Nabok, Alexei; Davis, Frank; Hassan, A.; Higson, Seamus P. J.; Evans-Freeman, J.CdS and ZnS semiconducting colloid nanoparticles coated with the organic shell, containing either SO3− or NH2+ groups, were prepared using the aqueous phase synthesis. The multilayer films of CdS (or ZnS) were deposited onto glass, quartz and silicon substrates using the technique of electrostatic self- assembly. The films produced were characterized with UV–vis spectroscopy, spectroscopic ellipsometry and atomic force microscopy. A substantial blue shift of the main absorption band with respect to the bulk materials was found for both CdS and ZnS films. The Efros equation in the effective mass approximation (EMA) theoretical model allowed the evaluation of the nanoparticle radius of 1.8 nm, which corresponds well to the ellipsometry results. AFM shows the formation of larger aggregates of nanoparticles on solid surfa