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X-ray fluorescence (XRF) spectroscopy was used to assess the effectiveness of various mild pretreatment methods for improving the fuel quality of banagrass, a tropical grass. Three types of pretreatment were used with increasing levels of severity: (i) S1 involves dewatering (pressing) only, (ii) S2 where the sample is pressed and leached, and (iii) S3 where pressing–leaching–pressing process is used. In addition, the influence of particle size (2 or 60–80 mm), leaching water temperature (25 or 75 °C), and leaching time (1 or 3 min) on the extraction of inorganic elements was examined. The results show that the S3 pretreatment is the most effective and that reducing the particle size has a more significant effect than increasing leaching temperature or time. Using a 2 mm particle size at 75 °C for 3 min produced the greatest effect, removing 50–60 wt % of the Na, ∼65 wt % Mg, ∼90 wt % P, ∼90 wt % K, ∼55 wt % S, and ∼95 wt % Cl. Using dewatering alone (S1) to pretreat the banagrass was the least effective ...

Quick and reliable inorganic elemental chemical analysis of biomass (including solid biofuels) is of importance in the increasing utilization and trade of biomass. In particular, it is important for the exploitation of contaminated/dirty biomass/biomass waste, and potentially also as a tool in ascertaining the type/origin of biomass. X-ray fluorescence (XRF) spectrometry performed directly on the raw biomass with limited prior sample preparation is an attractive method for performing such inorganic elemental analysis. In the present study, we therefore carefully investigate the performance of a commercial multielement standardless XRF method by analyzing five common biomass types (switchgrass, corn stover, eucalyptus, beech, and pine wood). Sample preparation involves milling the raw biomass using cutter and rotor mills (avoiding ball-milling) and coldpressing the powdered samples into pellets using wax binder. XRF users often rely on this type of commercial precalibrated or ‘standardless’ methods delivered with their XRF spectrometer. However, these methods are often sold without any guarantee on performance. We recently demonstrated the quite good performance of a typical commercial precalibrated/standardless method when analyzing biomass in the ideal form of certified reference material. In the present article, we report now on analysis of common raw biomass using the same method purchased with a 4 kW wavelength dispersive (WD) XRF spectrometer. The accuracy (trueness and precision) is determined by comparing the XRF data with the elemental composition obtained by standard elemental analysis (ICP-OES and ion-chromatography). The elements positively detected by the XRF are Na, Mg, Al, Si, P, S, Cl, K, Ca, Mn, Fe, Co, Ni, Cu, Zn, Sr, and maybe Mo. For elements above 25 ppm, the XRF data show a relative systematic error (bias, trueness) typically better than ±15% independent of the concentration. The elements present with >1000 ppm (Mg, Si, Cl, K, Ca) consistently show a positive bias of 3−18% relative. The relative precision (measured as the relative standard error) is better than ±5% (typically ±1%) for concentrations >25 ppm (obtained with 10−30 measurements). Quantifying elements below 25 ppm (Co, Ni, Cu, Zn, Sr, Mo) is possible in some cases, but it requires a more detailed study for each specific element. For example, Cu can be determined down to a few parts per million with an appropriate correction for the method bias. Occasionally, larger relative biases of up to 45−90% can occur for certain elements (Cl, Si) in certain samples, so care should be taken to carefully test the applied method for the particular samples and elements of interest. Quantification of silicon (Si) by XRF works well for concentrations >100 ppm. The XRF method can further be used to estimate the ash yield from biomass combustion with a relative bias better than ±10%. It is shown that the errors on the elemental composition are dominated by systematic errors (biases), and therefore, measuring the two sides of a single pellet combined with correction for any bias is the optimum approach. The five biomass types employed here, combined with the 13 certified reference materials employed in our previous study, span a broad range of biomass types with the XRF method generally producing reliable results (keeping in mind the limitations and needed bias corrections) with errors comparable to the standard reference methods. This suggests that typical standardless/precalibrated XRF methods work well in elemental analysis of raw biomass (keeping in mind the limitations) and therefore could be considered for general usage in, for example, industrial analytical laboratories requiring fast elemental analysis of biomass., JRC.F.2-Energy Conversion and Storage Technologies

An extended overview of the phase–mineral and chemical composition and classification of biomass ash (BA) was conducted. Some general considerations related to the composition of BA and particularly problems associated with this issue were discussed initially. Then, reference peer-reviewed data including phase–mineral composition and properties of BAs plus own investigations were used to describe and organise the BA system. It was found that BA is a complex inorganic–organic mixture with polycomponent, heterogeneous and variable composition. The phase–mineral composition of BA includes: (1) mostly inorganic matter composed of non-crystalline (amorphous) and crystalline to semi-crystalline (mineral) constituents; (2) subordinately organic matter consisting of char and organic minerals; and (3) some fluid matter comprising moisture and gas and gas–liquid inclusions associated with both inorganic and organic matter. Approximately 229 forming, major, minor or accessory phases or minerals were identified in BA. These species have primary, secondary or tertiary origin in the combustion residue and they are generated from natural (authigenic and detrital) and technogenic phases or minerals originally present in biomass. Common topics related to BA such as: terminology clarification; chemical composition; contents and concentration trends; correlations and associations; formation and behaviour; fusion temperatures; and leaching; were discussed and compared to coal ash. A general characterization of the phase–mineral composition and description of the occurrence and origin for common constituents in BA, namely: (1) silicates; (2) oxides and hydroxides; (3) sulphates (plus sulphides, sulphosalts, sulphites and thiosulphates); (4) phosphates; (5) carbonates (plus bicarbonates); (6) chlorides (plus chlorites and chlorates); (7) nitrates; (8) glass; (9) other inorganic phases; (10) organic phases; and (11) organic minerals; were also conducted and compared to coal ash. Finally, certain major associations related to the occurrence, content and origin of elements and phases were identified in the BA system and they include: (1) Si–Al–Fe–Na–Ti (mostly glass, silicates and oxyhydroxides); (2) Ca–Mg–Mn (commonly carbonates, oxyhydroxides, glass, silicates and some phosphates and sulphates); and (3) K–P–S–Cl (normally phosphates, sulphates, chlorides, glass and some silicates and carbonates). It was found that these systematic associations in BA have a key importance in both fundamental and applied aspects, namely their potential application for classification and indicator purposes connected with innovative and sustainable processing of BA. The potential utilization, technological and environmental advantages and challenges related to BA using the above classification approach are described in Part 2 of the present work.

An extended overview of the complex phase-mineral and chemical composition and properties of biomass ash (BA) was conducted in Part 1 of the present work. Then, the identified systematic associations, namely (1) Si–Al–Fe–Na–Ti (mostly glass, silicates and oxyhydroxides); (2) Ca–Mg–Mn (commonly carbonates, oxyhydroxides, glass, silicates and some phosphates and sulphates); and (3) K–P–S–Cl (normally phosphates, sulphates, chlorides, glass and some silicates and carbonates); connected with the occurrence, content and origin of elements and phases in the BA system were used for classification of BAs into four types and six sub-types in Part 1. The potential application of BA using the above classification approach is described in the present Part 2. It is demonstrated that such new BA classification has not only fundamental importance, but also has potential applications in prediction of properties and utilisation connected with the innovative and sustainable utilisation of BAs specified in different types and sub-types. The potential advantages and challenges related to utilisation of BA are described. Different aspects connected with BAs such as: (1) bulk utilisation (for soil amendment and fertilisation; production of construction materials, adsorbents, ceramics and other materials; plus synthesis of minerals); (2) recovery of valuable components and their utilisation (char, water-soluble, cenosphere–plerosphere, magnetic and heavy fractions; and elements); and (3) multicomponent utilisation; are described based on the reference investigations, present data and above classification. Subsequently, additional issues related to BAs, namely: (1) technological advantages and challenges (slagging, fouling and corrosion; low ash-fusion temperatures; erosion and abrasion; co-combustion and co-gasification; prediction of phase composition; and others); and (2) some environmental risks and health concerns (air, water, soil and plant contamination; acidity, alkalinity and leaching; volatilisation, retention, capture and immobilisation of hazardous elements and compounds; ash inhalation and disposal); during biomass and BA processing are also discussed. Finally, it is emphasised that the definitive utilisation, technological and environmental advantages and challenges related to BAs associate preferentially with specific BA types and sub-types and they could be predictable to some extent by using the above combined chemical and phase-mineral classification approaches.

An extended overview of the organic and inorganic phase composition of biomass was conducted. Some general considerations and problems related to phase composition of biomass as a solid fuel were discussed initially. Then, reference peer-reviewed data including contents of cellulose, hemicellulose, lignin and bulk extractives of 93 varieties of biomass were used and grouped for their comparison and classification. Additionally, reference peer-reviewed data and own investigations for various minor organic components and minerals, and modes of element occurrence identified in biomass were also applied and organised to describe the biomass systematically. It was found that the phase distinctions among the specified natural and anthropogenic (technogenic) biomass groups, sub-groups and varieties are significant and relate to different biomass sources and origin. The phase composition of biomass is highly variable due to the extremely high variations of structural components and different genetic types (authigenic, detrital and technogenic) of inorganic matter. The technogenic biomass group is quite complicated as a result of incorporation of various non-biomass materials during biomass processing. It was identified that the biomass phase composition is significantly different from that of coal. Correlations and associations among phase and chemical characteristics were studied to find some major trends and important relationships occurring in the natural biomass system. Certain leading associations related to the occurrence, content and origin of elements and phases in biomass were identified and discussed, namely: (1) C H (mainly as authigenic cellulose, hemicellulose, lignin and organic extractives); (2) Si Al Fe Na Ti (mostly as detrital silicates and oxyhydroxides, excluding authigenic opal); (3) Ca Mg Mn (commonly as authigenic oxalates and carbonates); and (4) N K S P Cl (normally as authigenic phosphates, sulphates, chlorides and nitrates). Finally, it was emphasised that these important associations have potential applications and can be used for initial classifications or prediction and indicator purposes connected with future advanced and sustainable processing of biomass to biofuels and chemical feedstock.

An extended overview of the chemical composition of biomass was conducted. The general considerations and some problems related to biomass and particularly the composition of this fuel are discussed. Reference peer-reviewed data for chemical composition of 86 varieties of biomass, including traditional and complete proximate, ultimate and ash analyses (21 characteristics), were used to describe the biomass system. It was shown that the chemical composition of biomass and especially ash components are highly variable due to the extremely high variations of moisture, ash yield, and different genetic types of inorganic matter in biomass. However, when the proximate and ultimate data are recalculated respectively on dry and dry ash-free basis, the characteristics show quite narrow ranges. In decreasing order of abundance, the elements in biomass are commonly C, O, H, N, Ca, K, Si, Mg, Al, S, Fe, P, Cl, Na, Mn, and Ti. It was identified that the chemical distinctions among the specified natural and anthropogenic biomass groups and sub-groups are significant and they are related to different biomass sources and origin, namely from plant and animal products or from mixtures of plant, animal, and manufacture materials. Respective chemical data for 38 solid fossil fuels were also applied as subsidiary information for clarifying the biomass composition and for comparisons. It was found that the chemical composition of natural biomass system is simpler than that of solid fossil fuels. However, the semi-biomass system is quite complicated as a result of incorporation of various non-biomass materials during biomass processing. It was identified that the biomass composition is significantly different from that of coal and the variations among biomass composition were also found to be greater than for coal. Natural biomass is: (1) highly enriched in Mn > K > P > Cl > Ca > (Mg, Na) > O > moisture > volatile matter; (2) slightly enriched in H; and (3) depleted in ash, Al, C, Fe, N, S, Si, and Ti in comparison with coal. The correlations and associations among 20 chemical characteristics are also studied to find some basic trends and important relationships occurring in the natural biomass system. As a result of that five strong and important associations, namely: (1) C–H; (2) N–S–Cl; (3) Si–Al–Fe–Na–Ti; (4) Ca–Mg–Mn; and (5) K–P–S–Cl; were identified and discussed. The potential applications of these associations for initial and preliminary classification, prediction and indicator purposes related to biomass were also introduced or suggested. However, future detailed data on the phase–mineral composition of biomass are required to explain actually such chemical trends and associations.

Udgivelsesdato: 2009-June-15 It has been widely reported that surface morphology on the micrometer scale affects cell function as well as cell shape. In this study, we have systematically compared the influence of 13 topographically micropatterned tantalum surfaces on the temporal development of morphology, including spreading, and length of preosteoblastic cells (MC3T3-E1). Cells were examined after 0.5, 1, 4, and 24 h on different Ta microstructures with vertical dimensions (heights) of 0.25 and 1.6 mum. Cell morphologies depended upon the underlying surface topography, and the length and spreading of cells varied as a function of time with regard to the two-dimensional pattern and vertical dimension of the structure. Microstructures of parallel grooves/ridges caused elongated cell growth after 1 and 4 h in comparison to a flat, nonstructured, reference surface. For microstructures consisting of pillars, cell spreading was found to depend on the distance between the pillars with one specific pillar structure exhibiting a decreased spreading combined with a radical change in morphology of the cells. Interestingly, this morphology on the particular pillar structure was associated with a markedly different distribution of the actin cytoskeleton. Our results provide a basis for further work toward topographical guiding of cell function. (c) 2008 Wiley Periodicals, Inc. J Biomed Mater Res, 2008.

Singlet oxygen has been detected in single nerve cells by its weak 1270 nm phosphorescence (a 1 Dg ! X 3 S 2 ) upon irradiation of a photosensitizer incorporated in the cell. Thus, one can now consider the application of direct optical imaging techniques to mechanistic studies of singlet oxygen at the single-cell level.

The regulatory Ni–Fe hydrogenase (RH) from Ralstonia eutropha which forms a [HoxBC] 2 complex functions as a hydrogen sensor under aerobic conditions. We have studied a novel Strep-tag isolate of the RH large subunit, HoxC ST , which lacks the Fe–S clusters of HoxB, allowing for structure determination of the catalytic site by X-ray absorption spectroscopy both at the Ni and, for the first time, also at the Fe K-edge. This technique, together with Fourier-transform infrared spectroscopy, revealed a Ni–Fe site with [O 1 (CysS) 2 Ni II (μ-SCys) 2 Fe II (CN) 2 (CO)] structure in about 50% of HoxC ST and a [(CysS) 2 Fe II (CN) 2 (CO)] site lacking Ni in the remainder protein. Possibly both sites may be intermediates in the maturation process of the RH.

Optical images of glassy, phase-separated polymer films have been generated using the 1270 nm phosphorescence of singlet molecular oxygen. Specifically, upon irradiation of immiscible blends of polystyrene and poly(ethylene-co-norbornene) that contain a singlet oxygen sensitizer, phase-separated droplets as small as ∼10 μm in diameter could be resolved using a microscope designed to detect singlet oxygen phosphorescence. This study demonstrates that it is possible to create singlet oxygen images of systems in which the sensitizer is not mobile (i.e., systems in which the effects of sensitizer bleaching cannot be rectified by diffusion of more dye into a given volume). The effect of singlet oxygen diffusion across the interfacial boundary between phase-separated domains of both liquid and polymer samples has also been examined. For singlet oxygen created in one phase, diffusion into a second phase in which the quantum yield of singlet oxygen phosphorescence is larger and oxygen is more soluble gives rise to a significant change in the intensity of the singlet oxygen signal at the interface. This effect can be pronounced when a long singlet oxygen lifetime facilitates singlet oxygen diffusion over large distances, but can be mitigated when interfacial tension yields a phase boundary with appreciable curvature. Boundary curvature in thin, phase-separated films of polystyrene/poly(ethylene-co-norbornene) is slight. Moreover, the singlet oxygen lifetime in these polymers is sufficiently short that, within its lifetime, singlet oxygen cannot diffuse over an appreciable distance. Under such conditions, singlet oxygen images of interfacial boundaries are sufficiently sharp as to make this optical technique useful for a range of fundamental studies.

A step-scan Fourier transform (FT) near infrared (IR) spectrometer has been used to record nanosecond time-resolved absorption spectra of singlet molecular oxygen (a1Δg→b1Σg+) created by pulsed-laser irradiation of a photosensitizer dissolved in a solvent. In addition to oxygen’s a→b transition at ∼5200 cm−1, other laser-induced changes in absorbance can be monitored over the spectral range ∼4000–11 000 cm−1. These include transients derived from the singlet oxygen sensitizer, and examples are provided with triplet state absorption spectra of several molecules in benzene as well as water. In this report, issues pertinent to the use of a step-scan FT spectrometer to monitor weak laser-induced near-IR signals are discussed. Specifically, key modifications to a commercially available instrument are described, and the relevant sources of noise from electronic components are outlined. Transient laser-induced thermal effects such as thermal lenses and temperature-dependent shifts in solvent absorption bands can...

The time-resolved absorption spectrum of singlet molecular oxygen (a1Δg → b1Σg+) has been recorded in liquid D2O using a step-scan Fourier transform spectrometer. A molar absorption coefficient of 6 ± 2 M-1 cm-1 was determined for the peak of the absorption band at 5228 ± 6 cm-1. In this report, issues pertinent to the detection of this signal are outlined. Specifically, for O2(a1Δg) produced upon pulsed laser irradiation of a sensitizer, it is necessary to account for a laser-induced, temperature-dependent shift in a D2O absorption band that interferes with the weak a → b signal. Along with a → b absorption coefficients obtained previously in other solvents, the D2O data reported herein enable an appropriate test of a topical model for the perturbing effect of solvent on radiative transitions in oxygen.

In a time-resolved infrared spectroscopic study, the a1Δg → b1Σg+ absorption spectrum of molecular oxygen at ∼5200 cm-1 was recorded in 19 solvents using a step-scan Fourier transform infrared spectrometer. Solvent-dependent changes in the full width at half-maximum of this absorption band covered a range of ∼30 cm-1 and solvent-dependent changes in the position of the band maximum covered a range of ∼55 cm-1. When considered along with solvent-dependent O2(a1Δg) → O2(X3Σg-) emission data, the current results identify features that must be incorporated in computational models of the interaction between oxygen and the surrounding solvent. In particular, data presented herein clearly demonstrate the importance of considering the influence of equilibrium and nonequilibrium solvation when interpreting the effect of solvent on transitions between the X3Σg-, a1Δg, and b1Σg+ states of oxygen. The data indicate that the bandwidths of the O2(a1Δg) → O2(b1Σg+) and O2(a1Δg) → O2(X3Σg-) transitions principally reflec...

The time-resolved absorption spectrum of singlet oxygen [O2(a1Δg) → O2(b1Σg+)] has been recorded in the region ∼5100–5300 cm−1 from air-saturated polystyrene samples using a microscope attached to a step-scan Fourier transform IR spectrometer. Singlet oxygen signals were observed with a time resolution of ∼160 ns from sample volumes of ∼20 nL using moderate data-acquisition times. These data indicate that it is reasonable and worthwhile to consider the further development of a transmission microscope as a viable tool to create singlet oxygen images of inhomogeneous samples including samples of biological importance.

With the increasing utilization and trade of biomass, there is a growing need for quick and reliable quantitative chemical analysis of the inorganic elemental composition of biomass. X-ray fluorescence (XRF) spectrometry performed directly on the raw biomass with limited prior sample preparation is an attractive method to this end. However, reliable calibration of XRF spectrometers for universal multi-element analysis can be very hard to implement mainly due to problems with matrix corrections. XRF users thus often rely on commercial precalibrated or standardless methods delivered with their XRF spectrometer. These methods are often sold without any guarantee on performance. Given the actual frequent use of these methods, along with their potential as ready-to-use methods for multi-element analysis of biomass, we investigate here the performance of a typical commercial precalibrated/standardless method recently purchased with a 4 kW wavelength dispersive (WD) XRF spectrometer. The accuracy (trueness and precision) is determined by analyzing the certified inorganic elements in 13 certified reference materials (CRMs) of diverse vegetal/plant origin. The certified elements detected by the XRF are Na, Mg, Al, P, S, Cl, K, Ca, V, Cr, Mn, Fe, Ni, Cu, Zn, As, Rb, Sr, Mo, Ba, and Pb. The relative systematic error (bias, trueness) is typically better than ±20% for elements in the range 25 to 100 ppm, better than ±15% for the range 100 to 1000 ppm, and better than ±10% for concentrations above 1000 ppm. The relative precision (measured as the relative standard error) is better than ±5% (typically ±1−2%) for concentrations >25 ppm. Quantifying elements below 25 ppm is possible in some cases, but it requires a more detailed study for each specific element. Occasionally, larger relative biases of up to ±40% can occur for certain elements in certain samples, so care has to be taken to carefully test the applied method for the particular samples and elements of interest. The XRF method can further be used to estimate the ash yield from biomass combustion with a relative bias (trueness) typically better than ±15%. This involves the determination of silicon (Si) and titanium (Ti) by XRF. The choice of matrix composition in the matrix correction model and the influence of sample moisture and sample grain-size are also addressed. The instrument and method are described in detail allowing for comparisons with other similar XRF spectrometers often already available in industrial analytical laboratories., JRC.F.2-Cleaner energy

This work describes an analytical approach to determine changes in mass distributions and structural properties of biomass/coal co-gasification tars, after storage of these samples as a function of temperature, time and presence of ambient light. The samples examined were tars recovered during the co-gasification of pine and a sub bituminous coal (70:30 wt%). It is shown that the approach used was able to reveal even subtle differences in the tar, which occurred during its ageing under different storage conditions. Precipitation was observed to occur in the tars after 5 °C, and in the presence of ambient light. Size exclusion chromatography and laser desorption mass spectrometry revealed the presence of molecular masses from 2000 u in the tars. UV-fluorescence spectroscopy provided information on extents of (aromatic) conjugation, providing evidence of sizes of fused-aromatic systems in these tars up to at least 8 rings. The study revealed that the molecules that contained the largest conjugated aromatic ring systems, rather than the molecules with the greatest masses, were primarily involved in the ageing reactions, resulting in precipitation occurring. Different ageing mechanisms were identified depending on whether the tar was stored cold (5°C) in the dark, at room temperature in the dark or in presence of ambient light., JRC.F.2-Cleaner energy

Upon irradiation of a photosensitizer, singlet molecular oxygen has been detected via its a1Δg → X3Σg- phosphorescence with a microscope. Using this tool, a singlet oxygen image with 2.5 μm resolution has been constructed of a phase-separated toluene/water mixture. For the a → X transition at ∼ 7850 cm-1 (∼ 1270 nm), a lateral resolution of 2.5 μm is close to the diffraction limit of ∼1.5−2.0 μm.

The quartz crystal microbalance with dissipation (QCM-D) technique was employed to characterize initial cell adhesion in terms of attachment and spreading of pre-osteoblastic MC3T3-E1 cells on Ta and Cr surfaces. Evaluation of initial cell adhesion established a correlation between input cell number and the shifts in frequency (f) and dissipation (D). The f-shift was found to be much larger in serum-free medium as compared to a medium including serum; hence, initial cell adhesion was subsequently evaluated in serum-free medium. During the first hour of adhesion, we found a positive correlation between the QCM-D f-shift and the average area of the spread cells, as measured by cryo-scanning electron microscopy (cryo-SEM). Finally, the QCM-D technique was used to study cell adhesion on different metal oxide surfaces. Initial cell adhesion on Ta was found to induce a larger f-shift as compared to Cr, indicating larger spreading of cells on Ta. Cryo-SEM data confirmed that spreading of cells on Cr was on average only two-thirds the spreading on Ta. Our results demonstrate that the QCM-D technique is a versatile technique to quickly distinguish initial cell-surface interactions on different biomaterials.

The regulatory Ni-Fe hydrogenase (RH) from Ralstonia eutropha functions as a hydrogen sensor. The RH consists of the large subunit HoxC housing the Ni-Fe active site and the small subunit HoxB containing Fe-S clusters. The heterolytic cleavage of H(2) at the Ni-Fe active site leads to the EPR-detectable Ni-C state of the protein. For the first time, the simultaneous but EPR-invisible reduction of Fe-S clusters during Ni-C state formation was demonstrated by changes in the UV-visible absorption spectrum as well as by shifts of the iron K-edge from x-ray absorption spectroscopy in the wild-type double dimeric RH(WT) [HoxBC](2) and in a monodimeric derivative designated RH(stop) lacking the C-terminal 55 amino acids of HoxB. According to the analysis of iron EXAFS spectra, the Fe-S clusters of HoxB pronouncedly differ from the three Fe-S clusters in the small subunits of crystallized standard Ni-Fe hydrogenases. Each HoxBC unit of RH(WT) seems to harbor two [2Fe-2S] clusters in addition to a 4Fe species, which may be a [4Fe-3S-3O] cluster. The additional 4Fe-cluster was absent in RH(stop). Reduction of Fe-S clusters in the hydrogen sensor RH may be a first step in the signal transduction chain, which involves complex formation between [HoxBC](2) and tetrameric HoxJ protein, leading to the expression of the energy converting Ni-Fe hydrogenases in R. eutropha.

Singlet oxygen has been detected in single nerve cells by its weak 1270 nm phosphorescence (a1deltag --> X3sigmag-) upon irradiation of a photosensitizer incorporated in the cell. Thus, one can now consider the application of direct optical imaging techniques to mechanistic studies of singlet oxygen at the single-cell level.

Magnetic AC mode (MACmode) atomic force microscopy (AFM) was used to study murine (mouse) MC3T3-E1 preosteoblastic cells attached to biocompatible tantalum substrates. Cell volumes of attached cells derived from AFM images were compared to volumes of detached cells in suspension measured by the Coulter sizing technique. An increase of approximately 50% in cell volume was observed when the cells attached to planar tantalum substrates and developed a flattened structure including lamellipodia. We address thoroughly the issues general to the AFM determination of absolute cell volumes, and compare our magnetic AC mode AFM measurements to hitherto reported cell volume determinations by contact mode AFM.