Blood Plasma Separation Using a Fidget-Spinner.

In this study, we present a simple, hand-powered, and electricity-free centrifuge platform based on a commercially available "fidget-spinner." The centrifugal force provided by this inexpensive and easy-to-use toy is sufficient to separate whole blood, producing a plasma yield rate and purity of 30% and 99%, respectively, separated in as little as 4-7 min. We verified the separated plasma by performing a paper-based HIV-1 p24 capsid protein enzyme-linked immunosorbent assay, which achieved a recovery rate of up to 98%, indicating the plasma features extremely low matrix interference effects. These results demonstrate the reliability of the platform for practical use, in addition to greatly reducing the overall cost and time of analysis while retaining detection precision, making it suitable for medical applications in resource-limited regions of the world.

A periodic array of nano-scale parallel slats for high-efficiency electroosmotic pumping.

It is known that the eletroosmotic (EO) flow rate through a nano-scale channel is extremely small. A channel made of a periodic array of slats is proposed to effectively promote the EO pumping, and thus greatly improve the EO flow rate. The geometrically simple array is complicated enough that four length scales are involved: the vertical period 2L, lateral period 2aL, width of the slat 2cL as well as the Debye length λD. The EO pumping rate is determined by the normalized lengths: a, c, or the perforation fraction of slats η=1-(c/a) and the dimensionless electrokinetic width K=L/λD. In a nano-scale channel, K is of order unity or less. EO pumping in both longitudinal and transverse directions (denoted as longitudinal EO pumping (LEOP) and transverse EO pumping (TEOP), respectively) is investigated by solving the Debye-Hückel approximation and viscous electro-kinetic equation. The main findings include that (i) the EO pumping rates of LEOP for small K are remarkably improved (by one order of magnitude) when we have longer slats (a≫1) and a large perforation fraction of slats (η > 0.7); (ii) the EO pumping rates of TEOP for small K can also be much improved but less significantly with longer slats and a large perforation fraction of slats. Nevertheless, it must be noted that in practice K cannot be made arbitrarily small as the criterion of φc≈0 for the reference potential at the channel center put lower bounds on K; in other words, there are geometrical limits for the use of the Poisson-Boltzmann equation.

Hybrid Machine Learning-Enabled Potential Energy Model for Atomistic Simulation of Lithium Intercalation into Graphite from Plating to Overlithiation.

Graphite is one of the most widely used negative electrode materials for lithium ion batteries (LIBs). However, because of the rapid growth of demands pursuing higher energy density and charging rates, comprehensive insights into the lithium intercalation and plating processes are critical for further boosting the potential of graphite electrodes. Herein, by utilizing the dihedral-angle-corrected registry-dependent potential (DRIP) (Wen et al., Phys. Rev. B 2018, 98, 235404), the Ziegler-Biersack-Littmark (ZBL) potential (Ziegler and Biersack, Astrophysics, Chemistry, and Condensed Matter; 1985, pp 93-129), and the machine learning-based spectral neighbor analysis (SNAP) potential (Thompson et al., J. Comput, Phys. 2015, 285, 316-330), we have successfully trained a hybrid machine learning-enabled potential energy model capable of simulating a wide spectrum of lithium intercalation scenario from plating to overlithiation. Our extensive atomistic simulations reveal the trapping of intercalated lithium atoms close to the graphite edges due to high hopping barriers, resulting in lithium plating. Furthermore, we report a stable dense graphite intercalation compound (GIC) LiC4 with a theoretical capacity of 558 mAh/g, wherein lithium atoms occupy alternating upper/lower graphene hollow sites with a nearest Li-Li distance of 2.8 Å. Surprisingly, following the same lithium insertion manner would allow the nearest Li-Li distance to be retained until the capacity reaches 845.2 mAh/g, corresponding to a GIC of LiC2.6. Hence, the present study demonstrates that the hybrid machine learning approach could further extend the scope of machine learning energy models, allowing us to investigate the lithium intercalation into graphite over a wide range of intercalation capacity to unveil the underlying mechanisms of lithium plating, diffusion, and discovery of new dense GICs for advanced LIBs with high charging rates and high energy densities.

Strain-compounding technique with ultrasound Nakagami imaging for distinguishing between benign and malignant breast tumors.

PURPOSE: The scatterer properties of breast tissues are related to the presence of collagen structures, while the elasticity properties of breast tissues depend on their structural organization; these two characteristics are functionally complementary in ultrasound-based tissue characterizations. This study investigated the use of a strain-compounding technique with Nakagami imaging to provide information associated with the scatterer and elasticity characteristics of tissues when attempting to identify benign and malignant breast tumors. METHODS: The efficacy of the proposed method was tested by collecting raw data of ultrasound backscattered signals from 50 clinical cases (25 benign tumors and 25 malignant tumors, as verified by histology biopsies). The different strain conditions were created by applying manual compression. For each region in which breast tumors were suspected, estimates of the full width at half maximum (FWHM) from the Gaussian fitting curve for the Nakagami-parameter histogram in the strain-compounding Nakagami images were divided by those of the corresponding reference Nakagami images (uncompressed images); this parameter was denoted as the FWHM ratio. Receiver operating characteristic (ROC) curve analysis was adopted to assess the diagnostic performance. RESULTS: The results demonstrated that the difference in scatterer distributions between before and after compounding was greater for benign tumors than for malignant tumors. The FWHM ratio estimates for benign and malignant tumors were 0.76 ± 0.14 and 0.96 ± 0.06 (mean ± standard deviation), respectively (p < 0.01). The mean area under the ROC curve using the FWHM ratio estimates was 0.92, with a 95% confidence interval of 0.83-1.00. CONCLUSIONS: These findings indicate that the strain-compounding Nakagami imaging method based on the acquisition of multiple frames under different strain states could provide objective information that would improve the ability to classify benign and malignant breast tumors.

The curvature index and synchronization of dynamical systems.

We develop a quantity, named the curvature index, for dynamical systems. This index is defined as the limit of the average curvature of the trajectory during evolution, which measures the bending of the curve on an attractor. The curvature index has the ability to differentiate the topological change of an attractor, as its alterations exhibit the structural changes of a dynamical system. Thus, the curvature index may indicate thresholds of some synchronization regimes. The Rössler system and a time-delay system are simulated to demonstrate the effectiveness of the index, respectively.

Interactive Somatosensory Games in Rehabilitation Training for Older Adults With Mild Cognitive Impairment: Usability Study.

BACKGROUND: In aging societies, dementia risk increases with advancing age, increasing the incidence of dementia-related degenerative diseases and other complications, especially fall risk. Dementia also escalates the care burden, impacting patients, their families, social welfare institutions, and the social structure and medical system. OBJECTIVE: In elderly dementia, traditional card recognition rehabilitation (TCRR) does not effectively increase one's autonomy. Therefore, from the usability perspective, we used the Tetris game as a reference to develop an interactive somatosensory game rehabilitation (ISGR) with nostalgic style for elders with mild cognitive impairment (MCI). Through intuitive gesture-controlled interactive games, we evaluated subjective feelings concerning somatosensory game integration into rehabilitation to explore whether the ISGR could improve the willingness to use and motivation for rehabilitation among elders with MCI. METHODS: A total of 15 elders with MCI (7 males and 8 females with an average age of 78.4 years) underwent 2 experiments for 15 minutes. During experiment 1, TCRR was performed, followed by completing the questionnaire of the System Usability Scale (SUS). After 3-5 minutes, the second experiment (the ISGR) was conducted, followed by completing another SUS. We used SUS to explore differences in impacts of TCRR and ISGR on willingness to use among elders with MCI. In addition, we further investigated whether the factor of gender or prior rehabilitation experience would affect the rehabilitation willingness or not. RESULTS: The novel ISGR made the elderly feel interested and improved their willingness for continuous rehabilitation. According to the overall SUS score, the ISGR had better overall usability performance (73.7) than the TCRR (58.0) (t28=-4.62, P<.001). Furthermore, the ISGR individual item scores of "Willingness to Use" (t28=-8.27, P<.001), "Easy to Use" (t28=-3.17, P<.001), "System Integration" (t28=-5.07, P<.001), and "Easy to Learn" (t28=-2.81, P<.001) were better than TCRR. The somatosensory game was easier to learn and master for females than for males (t13=2.71, P=.02). Besides, the ISGR was easier to use (t12=-2.50, P=.02) and learn (t14=-3.33, P<.001) for those without prior rehabilitation experience. The result indicates that for elders with no rehabilitation experience ISGR was easier to use and simpler to learn than TCRR. CONCLUSIONS: Regardless of prior rehabilitation experience, the ISGR developed in this study was easy to learn and effective in continuously improving willingness to use. Furthermore, the adoption of a nostalgic game design style served the function of cognitive training and escalated interest in rehabilitation. The ISGR also improved user stickiness by introducing different game scenarios and difficulties, increasing long-term interest and motivation for rehabilitation. For future research on the adoption of interactive somatosensory games in rehabilitation, additional rehabilitation movements can be developed to benefit the elderly with MCI.

Integrin molecular tension required for focal adhesion maturation and YAP nuclear translocation.

Focal adhesions (FAs) provide the cells linkages to extracellular matrix (ECM) at sites of integrins binding and transmit mechanical forces between the ECM and the actin cytoskeleton. Cells sense and respond to physical stimuli from their surrounding environment through the activation of mechanosensitive signaling pathways, a process called mechanotransduction. In this study, we used RGD-peptide conjugated DNA tension gauge tethers (TGTs) with different tension tolerance (Ttol) to determine the molecular forces required for FA maturation in different sizes and YAP nuclear translocation. We found that the limitation of FA sizes in cells seeded on TGTs with different Ttol were less than 1 µm, 2 µm, 3 µm, and 6 µm for Ttol values of 43 pN, 50 pN, 54 pN, and 56 pN, respectively. This suggests that the molecular tension across integrins increases gradually as FA size increases throughout FA maturation. For YAP nuclear translocation, significant YAP nuclear localization was observed only in the cells seeded on the TGTs with Ttol ≥ 54 pN, but not on TGTs with Ttol ≤ 50 pN, suggesting a threshold of molecular force across integrins for YAP nuclear translocation lies in the range of 50 pN-54 pN.

Electro-osmotic flow in polygonal ducts.

The paper presents semi-analytical solutions to electro-osmotic (EO) flow through polygonal ducts under the Debye-Hückel approximation. Analytical series solutions assisted with numerical collocations are found to yield very fast convergence. The solutions have practical applications as the pores of EO membranes are mostly hexagonal, stacked densely in a beehive-like matrix. In addition, we develop simple asymptotic approximations that would be applicable to all EO tube flows of small as well as large dimensionless electrokinetic width. This facilitates investigation of analytical structures of general EO flows in all shapes of tubes, including the present geometries. In particular, for thick electrical double layers, the flow rate of EO is related to the corresponding viscous Poiseuille flow rate, while for thin electrical double layers, the flow rate is shown to be characterized by the cross-sectional area and the perimeter length of the tubes.

Classification of scattering media within benign and malignant breast tumors based on ultrasound texture-feature-based and Nakagami-parameter images.

PURPOSE: Benign and malignant tumors can be classified by using texture analysis of the ultrasound B-scan image to describe the variation in the echogenicity of scatterers. The recently proposed ultrasonic Nakagami parametric image has also been used to detect the concentrations and arrangements of scatterers for tumor characterization applications. B-scan-based texture analysis and the Nakagami parametric image are functionally complementary in ultrasonic tissue characterizations and this study aimed to combine these methods in order to improve the ability to characterize breast tumors. METHODS: To validate this concept, radio-frequency data obtained from 130 clinical cases were used to construct the texture-feature parametric image and the Nakagami parametric image. Four texture-feature parameters based on a gray-level co-occurrence matrix (homogeneity, contrast, energy, and variance) and the Nakagami parameters of the benign and malignant tumors were calculated. The usefulness of an individual parameter was determined and scatter graphs indicated the relationship between two selected texture-feature parameters. Fisher's linear discriminant analysis was used to combine the selected texture-feature parameters with the Nakagami parameter. The performance in classifying tumors was evaluated based on the receiver operating characteristic curve. RESULTS: The results indicated that there is a trade-off between sensitivity and specificity when using an individual texture-feature parameter or when combining two such correlated parameters to discriminate benign and malignant cases. However, the best performance was obtained when combining selected texture-feature parameters with the Nakagami parameter. CONCLUSIONS: The study findings suggest that combining B-scan-based texture analysis and the Nakagami parametric image could improve the ability to classify benign and malignant breast tumors.

Microstructure Maps of Complex Perovskite Materials from Extensive Monte Carlo Sampling Using Machine Learning Enabled Energy Model.

Revealing the process-structure-property (PSP) relationships of chemically complex mixed-ion perovskite requires comprehensive insights into correlations between microstructures and chemical compositions. However, experimentally determining the microstructural information about complex perovskites over the composition space is a challenging task. In this study, a machine learning enabled energy model was trained for MAyFA1-yPb(BrxI1-x)3 mixed-ion perovskite for fast and extensive sampling over the compositional/permutational spaces to map the ion-mixing energies, chemical ordering, and atomic strains. Correlation analysis indicated the strong lattice distortion in the high-MA/Br concentration regime is the primary reason for poor device performance-strong lattice distortion induces high mixing energy, resulting in phase segregation and defect formation. Hence, mitigating lattice distortion to retain the single-phase solid solution is one necessary condition of the optimal composition of mixed-ion perovskites. The present study therefore provides insights into the microstructures as well as the guidelines for determining the optimal composition of mixed-ion perovskite materials.

Molecular dynamics simulations of the rotary motor F(0) under external electric fields across the membrane.

The membrane-bound component F(0), which is a major component of the F(0)F(1)-ATP synthase, works as a rotary motor and plays a central role in driving the F(1) component to transform chemiosmotic energy into ATP synthesis. We conducted molecular dynamics simulations of b(2)-free F(0) in a 1-palmitoyl-2-oleoyl-phosphatidylcholine lipid bilayer for tens of nanoseconds with two different protonation states of the cAsp-61 residue at the interface of the a-c complex in the absence of electric fields and under electric fields of +/-0.03 V/nm across the membrane. To our surprise, we observed that the upper half of the N-terminal helix of the c(1) subunit rotated about its axis clockwise by 30 degrees . An energetic analysis revealed that the electrostatic repulsion between this N-terminal helix and subunit c(12) was a major contributor to the observed rotation. A correlation map analysis indicated that the correlated motions of residues in the interface of the a-c complex were significantly reduced by external electric fields. The deuterium order parameter (S(CD)) profile calculated by averaging all the lipids in the F(0)-bound bilayer was not very different from that of the pure bilayer system, in agreement with recent (2)H solid-state NMR experiments. However, by delineating the lipid properties according to their vicinity to F(0), we found that the S(CD) profiles of different lipid shells were prominently different. Lipids close to F(0) formed a more ordered structure. Similarly, the lateral diffusion of lipids on the membrane surface also followed a shell-dependent behavior. The lipids in the proximity of F(0) exhibited very significantly reduced diffusional motion. The numerical value of S(CD) was anticorrelated with that of the diffusion coefficient, i.e., the more ordered lipid structures led to slower lipid diffusion. Our findings will help elucidate the dynamics of F(0) depending on the protonation state and electric field, and may also shed some light on the interactions between the motor F(0) and its surrounding lipids under physiological conditions, which could help to rationalize its extraordinary energy conversion efficiency.

Mixed-mode electrokinetic and chromatographic peptide separations in a microvalve-integrated polymer chip.

A cycloolefin polymer chip supporting the concatenation of isoelectric focusing (IEF) and reversed-phase liquid chromatography (RPLC) is demonstrated for high throughput two dimensional peptide separations. A unique benefit of the mixed-mode platform is the ability of IEF to act as a highly concentrating electrokinetic separation mode for effective isolation of sample components prior to RPLC. The thermoplastic chip contains integrated high pressure microvalves, enabling uniform sample transfer from the IEF channel to multiple parallel RPLC channels, gradient elution from each RPLC column, and hydrodynamic isolation between the separation dimensions. The reusable system is shown to provide efficient 2-D separations together with facile interfacing with MALDI-MS, suggesting a new path towards effective peptide analysis from complex samples.

High-pressure on-chip mechanical valves for thermoplastic microfluidic devices.

A facile method enabling the integration of elastomeric valves into rigid thermoplastic microfluidic chips is described. The valves employ discrete plugs of elastomeric polydimethylsiloxane (PDMS) integrated into the thermoplastic substrate and actuated using a threaded stainless steel needle. The fabrication process takes advantage of poly(ethylene glycol) (PEG) as a sacrificial molding material to isolate the PDMS regions from the thermoplastic flow channels, while yielding smooth contact surfaces with the PDMS valve seats. The valves introduce minimal dead volumes, and provide a simple mechanical means to achieve reproducible proportional valving within thermoplastic microfluidic systems. Burst pressure tests reveal that the valves can withstand pressures above 12 MPa over repeated open/close cycles without leakage, and above 24 MPa during a single use, making the technology well suited for applications such as high performance liquid chromatography. Proportional valve operation is demonstrated using a multi-valve chemical gradient generator fabricated in cyclic olefin polymer.

Polymer microchips integrating solid-phase extraction and high-performance liquid chromatography using reversed-phase polymethacrylate monoliths.

Polymer microfluidic chips employing in situ photopolymerized polymethacrylate monoliths for high-performance liquid chromatography separations of peptides is described. The integrated chip design employs a 15 cm long separation column containing a reversed-phase polymethacrylate monolith as a stationary phase, with its front end seamlessly coupled to a 5 mm long methacrylate monolith which functions as a solid-phase extraction (SPE) element for sample cleanup and enrichment, serving to increase both detection sensitivity and separation performance. In addition to sample concentration and separation, solvent splitting is also performed on-chip, allowing the use of a conventional LC pump for the generation of on-chip nanoflow solvent gradients. The integrated platform takes advantage of solvent bonding and a novel high-pressure needle interface which together enable the polymer chips to withstand internal pressures above 20 MPa (approximately 2900 psi) for efficient pressure-driven HPLC separations. Gradient reversed-phase separation of fluorescein-labeled model peptides and BSA tryptic digest are demonstrated using the microchip HPLC system. Online removal of free fluorescein and enrichment of labeled proteins are simultaneously achieved using the on-chip SPE column, resulting in a 150-fold improvement in sensitivity and a 10-fold reduction in peak width in the following microchip gradient LC separation.

Association between color doppler vascularity index, angiogenesis-related molecules, and clinical outcomes in gastric cancer.

PURPOSE: This study was conducted to evaluate the correlation between color Doppler vascularity index (CDVI), clinical outcomes and five angiogenesis-related molecules including vascular endothelial growth factor (VEGF), placenta growth factor (PlGF), cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), and calreticulin (CRT) in gastric cancer, and to develop an effective model selected from these five molecules to predict patient survival. PATIENTS AND METHODS: CDVI could be obtained preoperatively by transabdominal ultrasound from 30 patients. Enzyme immunoassay was adopted to determine protein level of VEGF and PlGF, and immunohistochemistry was used to detect COX-2, iNOS and CRT expression. Correlation between CDVI and five individual molecules was assessed. Multiple molecules model was developed using classification and regression tree (CART) analysis from five molecules, and was tested for patient survival in another 45 patients. RESULTS: CDVI was significantly correlated with patient survival (P = 0.00907) and absolute number of metastatic lymph nodes (P = 0.01). There was no significant association between CDVI and any individual molecule. The model, developed by CART consisting of VEGF and PlGF, could differentiate high and low CDVI and survival in testing group (P = 0.00257). CONCLUSIONS: CDVI was associated with lymph node metastasis, combined VEGF and PlGF expression status and patient survival in gastric cancer.

Instantaneous frequency as a new approach for evaluating the clinical severity of Duchenne muscular dystrophy through ultrasound imaging.

Duchenne muscular dystrophy (DMD) results in loss of ambulation for the patients. Ultrasound attenuation correlates with fat content in muscles, resulting in changes in signal frequency. The Hilbert-Huang transform (HHT) allows time-frequency analysis with high time-frequency resolution. This study explored the feasibility of using the instantaneous frequency (IF) obtained from the HHT to diagnose the walking function of patients with DMD. Eighty-five participants (12 control and 73 patients with DMD) underwent a standard-care ultrasound examination of the gastrocnemius to acquire raw image data for ultrasound B-mode and IF calculations, which were compared with the DMD stage using Pearson correlation and receiver operating characteristic (ROC) curve analyses. With increasing DMD stage, the median IF decreased from 7.25 to 7.01 MHz (the correlation coefficient r = -0.73; the probability value p < 0.0001). The area under the ROC curve was 0.97 when using ultrasound IF to discriminate between ambulatory and nonambulatory patients (accuracy: 91.76%; sensitivity: 93.75%; and specificity: 90.57%). The study reveals that ultrasound IF has great potential in DMD evaluation and management.

Classification of breast masses by ultrasonic Nakagami imaging: a feasibility study.

Ultrasound is an important clinical tool in noninvasive diagnoses of breast cancer. The Nakagami statistical parameter estimated from the ultrasonic backscattered envelope has been demonstrated to be useful in complementing conventional B-mode scans when classifying breast masses. However, the shadowing effect caused by certain high-attenuation tumors in the B-mode image makes the tumor contour unclear, and thus it is more difficult to choose an appropriate region of interest from which to collect tumor data for estimating the Nakagami parameter. This study explored the feasibility of using the Nakagami parametric image to overcome the shadowing effect for visualizing the properties of breast masses. Experiments were performed on a breast-mimicking phantom and on some typical clinical cases for cysts, fat and tumors (fibroadenoma) (n = 18) in order to explore the performance of the Nakagami image under ideal and practical conditions. The experimental results showed that the Nakagami image pixels (i.e. the local Nakagami parameter) in the cyst, tumor and fat are 0.21 +/- 0.01, 0.65 +/- 0.05 and 0.98 +/- 0.07, respectively, for six independent phantom measurements, and 0.14 +/- 0.03, 0.67 +/- 0.11 and 0.89 +/- 0.08, respectively, for clinical experiments. This suggests that the Nakagami image is able to classify various breast masses (p < 0.005) although the clinical results from tumors of different cases have a larger variance that may be caused by the complexity of real breast tissues. In particular, unlike the B-mode image, the Nakagami image is not subject to significant shadowing effects, making it useful to complement the B-mode image to describe the tumor contour for identifying the tumor-related region when the shadowing effect is stronger or a low system gain is used.

Feasibility study of using high-frequency ultrasonic Nakagami imaging for characterizing the cataract lens in vitro.

A cataract is a clouding of the crystalline lens that reduces the amount of incoming light and impairs visual perception. Phacoemulsification is the most common surgical method for treating advanced cataracts, and determining the optimal phacoemulsification energy is dependent on measuring the hardness of the lens. This study explored the feasibility of using an ultrasonic parametric image based on the Nakagami distribution to quantify the lens hardness. Young's modulus was measured in porcine lenses in which cataracts had been artificially induced. High-frequency ultrasound at 35 MHz was used to obtain the B-mode and Nakagami images of the cataract lenses. The averaged integrated backscatter and Nakagami parameters were also estimated in the region of interest. The experimental results show that the conventional B-scan and integrated backscatter are inadequate for quantifying the lens hardness, whereas Nakagami imaging allows different degrees of lens hardening to be distinguished both globally and locally based on the concentration of fiber coemption therein.

Imaging local scatterer concentrations by the Nakagami statistical model.

The ultrasonic B-mode image is an important clinical tool used to examine the internal structures of the biological tissue. Due to the fact that the conventional B-scans cannot fully reflect the nature of the tissue, some useful quantitative parameters have been applied to quantify the properties of the tissue. Among various possibilities, the Nakagami parameter was demonstrated to have an outstanding ability to detect the variation of the scatterer concentration. This study is aimed to develop a scatterer concentration image based on the Nakagami parameter map to assist in the B-mode image for tissue characterization. In particular, computer simulations are carried out to generate phantoms of different scatterer concentrations and echogenicity coefficients and their B-mode and Nakagami parametric images are compared to evaluate the performance of the Nakagami image in differentiating the properties of the scatterers. The simulated results show that the B-mode image would be affected by the system settings and user operations, whereas the Nakagami parametric image provides a comparatively consistent image result when different diagnosticians use different dynamic ranges and system gains. This is largely because the Nakagami image formation is only based on the backscattered statistics of the ultrasonic signals in local tissues. Such an imaging principle allows the Nakagami image to quantify the local scatterer concentrations in the tissue and to extract the backscattering information from the regions of the weaker echoes that may be lost in the B-mode image. These findings suggest that the Nakagami image can be combined with the use of the B-mode image simultaneously to visualize the tissue structures and the scatterer properties for a better medical diagnosis.

Particle plasmons of metal nanospheres: application of multiple scattering approach.

In this paper, we study particle plasmons associated with a chain of metal nanospheres by the method of multiple scattering. The extinction efficiency is used to identify the resonant modes in nanoparticle chains. Special emphasis is placed upon the multipolar nature of particle plasmons at two major resonant modes by studying the associated field patterns, surface charges, and distributions of the field enhancement. Effects of the number of particles, interparticle spacing, and particle alignment are investigated by examining the frequency shift, bandwidth, and the number of resonant modes.