{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,1]],"date-time":"2026-10-01T02:09:28Z","timestamp":1790820568121,"version":"4.1.0"},"reference-count":41,"publisher":"MDPI AG","issue":"5","license":[{"start":{"date-parts":[[2021,5,19]],"date-time":"2021-05-19T00:00:00Z","timestamp":1621382400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Viruses"],"abstract":"<jats:p>Virus particle concentration is a critical piece of information for virology, viral vaccines and gene therapy research. We tested a novel nanoparticle counting device, \u201cVideodrop\u201d, for its efficacy in titering and characterization of virus particles. The Videodrop nanoparticle counter is based on interferometric light microscopy (ILM). The method allows the detection of particles under the diffraction limit capabilities of conventional light microscopy. We analyzed lenti-, adeno-, and baculovirus samples in different concentrations and compared the readings against traditional titering and characterization methods. The tested Videodrop particle counter is especially useful when measuring high-concentration purified virus preparations. Certain non-purified sample types or small viruses may be impossible to characterize or may require the use of standard curve or background subtraction methods, which increases the duration of the analysis. Together, our testing shows that Videodrop is a reasonable option for virus particle counting in situations where a moderate number of samples need to be analyzed quickly.<\/jats:p>","DOI":"10.3390\/v13050939","type":"journal-article","created":{"date-parts":[[2021,5,19]],"date-time":"2021-05-19T21:49:21Z","timestamp":1621460961000},"page":"939","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":26,"title":["Experimental Evaluation of an Interferometric Light Microscopy Particle Counter for Titering and Characterization of Virus Preparations"],"prefix":"10.3390","volume":"13","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-9626-1966","authenticated-orcid":false,"given":"Vesa","family":"Turkki","sequence":"first","affiliation":[{"name":"Kuopio Center for Gene and Cell Therapy, 70210 Kuopio, Finland"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Elisa","family":"Alppila","sequence":"additional","affiliation":[{"name":"Kuopio Center for Gene and Cell Therapy, 70210 Kuopio, Finland"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7593-2708","authenticated-orcid":false,"given":"Seppo","family":"Yl\u00e4-Herttuala","sequence":"additional","affiliation":[{"name":"Molecular Medicine Research Group, A.I. Virtanen Institute for Molecular Sciences, University of Eastern Finland, 70210 Kuopio, Finland"},{"name":"Heart Center and Gene Therapy Unit, Kuopio University Hospital, 70210 Kuopio, Finland"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hanna P.","family":"Lesch","sequence":"additional","affiliation":[{"name":"Kuopio Center for Gene and Cell Therapy, 70210 Kuopio, Finland"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2021,5,19]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"475","DOI":"10.1099\/0022-1317-34-3-475","article-title":"Characteristics of the Microplate Method of Enzyme-Linked Immunosorbent Assay for the Detection of Plant Viruses","volume":"34","author":"Clark","year":"1977","journal-title":"J. Gen. Virol."},{"key":"ref_2","doi-asserted-by":"crossref","unstructured":"Geraerts, M., Willems, S., Baekelandt, V., Debyser, Z., and Gijsbers, R. (2006). Comparison of lentiviral vector titration methods. BMC Biotechnol., 6.","DOI":"10.1186\/1472-6750-6-34"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"453","DOI":"10.1089\/hum.1997.8.4-453","article-title":"Analytical Anion-Exchange HPLC of Recombinant Type-5 Adenoviral Particles","volume":"8","author":"Shabram","year":"1997","journal-title":"Hum. Gene Ther."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"180","DOI":"10.1038\/sj.gt.3302851","article-title":"High-performance liquid chromatography method for rapid assessment of viral particle number in crude adenoviral lysates of mixed serotype","volume":"14","author":"Kuhn","year":"2006","journal-title":"Gene Ther."},{"key":"ref_5","first-page":"34","article-title":"Viral Vector Particle Integrity and Purity Analysis in Early Process Development","volume":"15","author":"Turkki","year":"2017","journal-title":"Bioprocess Int."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"e2019","DOI":"10.1002\/rmv.2019","article-title":"Virus detection by transmission electron microscopy: Still useful for diagnosis and a plus for biosafety","volume":"29","author":"Roingeard","year":"2019","journal-title":"Rev. Med Virol."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"268","DOI":"10.1128\/MMBR.00041-10","article-title":"Atomic Force Microscopy in Imaging of Viruses and Virus-Infected Cells","volume":"75","author":"Kuznetsov","year":"2011","journal-title":"Microbiol. Mol. Biol. Rev."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"796","DOI":"10.1007\/s11095-010-0073-2","article-title":"Critical Evaluation of Nanoparticle Tracking Analysis (NTA) by NanoSight for the Measurement of Nanoparticles and Protein Aggregates","volume":"27","author":"Filipe","year":"2010","journal-title":"Pharm. Res."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"265","DOI":"10.1186\/1743-422X-9-265","article-title":"Evaluation of nanoparticle tracking analysis for total virus particle determination","volume":"9","author":"Kramberger","year":"2012","journal-title":"Virol. J."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"235","DOI":"10.1089\/hgtb.2019.172","article-title":"Nanoparticle Tracking of Adenovirus by Light Scattering and Fluorescence Detection","volume":"30","author":"Gast","year":"2019","journal-title":"Hum. Gene Ther. Methods"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"1500","DOI":"10.3389\/fmicb.2016.01500","article-title":"Quantification of Virus Particles Using Nanopore-Based Resistive-Pulse Sensing Techniques","volume":"7","author":"Yang","year":"2016","journal-title":"Front. Microbiol."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"251","DOI":"10.1007\/s12033-017-0009-8","article-title":"Integrated Method for Purification and Single-Particle Characterization of Lentiviral Vector Systems by Size Exclusion Chromatography and Tunable Resistive Pulse Sensing","volume":"59","author":"Heider","year":"2017","journal-title":"Mol. Biotechnol."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"1858","DOI":"10.1002\/1873-3468.12186","article-title":"Super-resolved insights into human immunodeficiency virus biology","volume":"590","author":"Hanne","year":"2016","journal-title":"FEBS Lett."},{"key":"ref_14","first-page":"e01765-17","article-title":"Flow Virometry: A Powerful Tool to Functionally Characterize Viruses","volume":"92","year":"2017","journal-title":"J. Virol."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"87","DOI":"10.1016\/j.ymeth.2017.12.011","article-title":"Flow virometry as a tool to study viruses","volume":"134\u2013135","author":"Zamora","year":"2018","journal-title":"Methods"},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"857","DOI":"10.3390\/v7030857","article-title":"Evaluation of ViroCyt\u00ae Virus Counter for Rapid Filovirus Quantitation","volume":"7","author":"Rossi","year":"2015","journal-title":"Viruses"},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"3736","DOI":"10.1364\/BOE.7.003736","article-title":"Full-field interferometry for counting and differentiating aquatic biotic nanoparticles: From laboratory to Tara Oceans","volume":"7","author":"Boccara","year":"2016","journal-title":"Biomed. Opt. Express"},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"413","DOI":"10.1016\/j.resmic.2017.02.004","article-title":"Utilization of interferometric light microscopy for the rapid analysis of virus abundance in a river","volume":"168","author":"Fedala","year":"2017","journal-title":"Res. Microbiol."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"39","DOI":"10.1038\/gt.2017.91","article-title":"Optimization of lentiviral vector production for scale-up in fixed-bed bioreactor","volume":"25","author":"Valkama","year":"2018","journal-title":"Gene Ther."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"63","DOI":"10.1016\/j.omtm.2019.08.006","article-title":"Preclinical Proof-of-Concept, Analytical Development, and Commercial Scale Production of Lentiviral Vector in Adherent Cells","volume":"15","author":"Leinonen","year":"2019","journal-title":"Mol. Ther. Methods Clin. Dev."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"717","DOI":"10.1016\/j.omtm.2020.03.025","article-title":"Development of Large-Scale Downstream Processing for Lentiviral Vectors","volume":"17","author":"Valkama","year":"2020","journal-title":"Mol. Ther. Methods Clin. Dev."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"376","DOI":"10.1089\/hum.2019.247","article-title":"Benchmarking of Scale-X Bioreactor System in Lentiviral and Adenoviral Vector Production","volume":"31","author":"Leinonen","year":"2020","journal-title":"Hum. Gene Ther."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"560","DOI":"10.1089\/hum.2015.081","article-title":"Process Development of Adenoviral Vector Production in Fixed Bed Bioreactor: From Bench to Commercial Scale","volume":"26","author":"Lesch","year":"2015","journal-title":"Hum. Gene Ther."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"1280","DOI":"10.1038\/gt.2008.76","article-title":"Generation of Lentivirus Vectors Using Recombinant Baculoviruses","volume":"15","author":"Lesch","year":"2008","journal-title":"Gene Ther."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"1499","DOI":"10.1038\/sj.gt.3301269","article-title":"Baculovirus-mediated periadventitial gene transfer to rabbit carotid artery","volume":"7","author":"Airenne","year":"2000","journal-title":"Gene Ther."},{"key":"ref_26","doi-asserted-by":"crossref","unstructured":"Airenne, K.J., Peltomaa, E., Hyt\u00f6nen, V.P., Laitinen, O.H., and Yl\u00e4-Herttuala, S. (2003). Improved generation of recombinant baculovirus genomes in Escherichia coli. Nucleic Acids Res., 31.","DOI":"10.1093\/nar\/gng102"},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"8463","DOI":"10.1128\/JVI.72.11.8463-8471.1998","article-title":"A third-generation lentivirus vector with a conditional packaging system","volume":"72","author":"Dull","year":"1998","journal-title":"J. Virol."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"25","DOI":"10.12665\/J11.Hutchins","article-title":"Development of a Reference Material for Characterizing Adenovirus Vectors","volume":"1","author":"Hutchins","year":"2002","journal-title":"Bioprocess. J."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"96","DOI":"10.1089\/hgtb.2017.198","article-title":"Determination of Lentiviral Infectious Titer by a Novel Droplet Digital PCR Method","volume":"29","author":"Wang","year":"2018","journal-title":"Hum. Gene Ther. Methods"},{"key":"ref_30","doi-asserted-by":"crossref","unstructured":"Motulsky, H.J., and Brown, R.E. (2006). Detecting outliers when fitting data with nonlinear regression\u2014A new method based on robust nonlinear regression and the false discovery rate. BMC Bioinform., 7.","DOI":"10.1186\/1471-2105-7-123"},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"518","DOI":"10.1007\/BF01962603","article-title":"Inactivation of human immunodeficiency virus in serum specimens as a safety measure for diagnostic immunoassays","volume":"7","author":"Ukkonen","year":"1988","journal-title":"Eur. J. Clin. Microbiol. Infect. Dis."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"928","DOI":"10.1128\/JCM.02045-09","article-title":"Influenza Virus Inactivation for Studies of Antigenicity and Phenotypic Neuraminidase Inhibitor Resistance Profiling","volume":"48","author":"Jonges","year":"2010","journal-title":"J. Clin. Microbiol."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"907.e7","DOI":"10.1016\/j.cmi.2018.10.016","article-title":"Effective chemical virus inactivation of patient serum compatible with accurate serodiagnosis of infections","volume":"25","author":"Remy","year":"2019","journal-title":"Clin. Microbiol. Infect."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"S5","DOI":"10.1038\/sj.gt.3302611","article-title":"Chromatographic purification of recombinant adenoviral and adeno-associated viral vectors: Methods and implications","volume":"12","author":"Burova","year":"2005","journal-title":"Gene Ther."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"977","DOI":"10.1128\/jvi.39.3.977-980.1981","article-title":"Adenovirus type 5 virions can be assembled in vivo in the absence of detectable polypeptide IX","volume":"39","author":"Colby","year":"1981","journal-title":"J. Virol."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"1570","DOI":"10.1038\/sj.gt.3301285","article-title":"Ammonium sulphate precipitation of recombinant adenovirus from culture medium: An easy method to increase the total virus yield","volume":"7","author":"Schagen","year":"2000","journal-title":"Gene Ther."},{"key":"ref_37","doi-asserted-by":"crossref","unstructured":"Shabram, P.W., Vellekamp, G., Ruan, Q., and Scandella, C. (2016). Purification of Adenovirus. Adenoviral Vectors for Gene Therapy, Elsevier. [2nd ed.].","DOI":"10.1016\/B978-0-12-800276-6.00008-5"},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"617","DOI":"10.1038\/nprot.2016.022","article-title":"Interferometric scattering microscopy and its combination with single-molecule fluorescence imaging","volume":"11","author":"Arroyo","year":"2016","journal-title":"Nat. Protoc."},{"key":"ref_39","doi-asserted-by":"crossref","unstructured":"Gonz\u00e1lez-Dom\u00ednguez, I., Puente-Massaguer, E., Cervera, L., and G\u00f2dia, F. (2020). Quality Assessment of Virus-Like Particles at Single Particle Level: A Comparative Study. Viruses, 12.","DOI":"10.3390\/v12020223"},{"key":"ref_40","doi-asserted-by":"crossref","unstructured":"Vogel, R., Savage, J., Muzard, J., Della Camera, G., Vella, G., Law, A., Marchioni, M., Mehn, D., Geiss, O., and Peacock, B. (2021). Measuring particle concentration of multimodal synthetic reference materials and extracellular vesicles with orthogonal techniques: Who is up to the challenge?. J. Extracell. Vesicles, 10.","DOI":"10.1002\/jev2.12052"},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"199","DOI":"10.1016\/j.virol.2014.06.005","article-title":"Quantitative real-time single particle analysis of virions","volume":"462\u2013463","author":"Heider","year":"2014","journal-title":"Virology"}],"container-title":["Viruses"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1999-4915\/13\/5\/939\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T06:04:01Z","timestamp":1760162641000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1999-4915\/13\/5\/939"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2021,5,19]]},"references-count":41,"journal-issue":{"issue":"5","published-online":{"date-parts":[[2021,5]]}},"alternative-id":["v13050939"],"URL":"https:\/\/doi.org\/10.3390\/v13050939","relation":{},"ISSN":["1999-4915"],"issn-type":[{"value":"1999-4915","type":"electronic"}],"subject":[],"published":{"date-parts":[[2021,5,19]]}}}