1 Carbon nanotube substrates enhance SARS -CoV-2 spike protein ion yields in matrix assisted laser desorption -ionization mass spectrometry

2025-04-28 0 0 1.29MB 10 页 10玖币

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Carbon nanotube substrates enhance SARS-CoV-2 spike protein ion yields in matrix assisted

laser desorption-ionization mass spectrometry

T. Schenkel1, A. M. Snijders2, K. Nakamura1, P.A. Seidl1, B. Mak1, L. Obst-Huebl1, H. Knobel3, I. Pong1, A.

Persaud1, J. van Tilborg1, T. Ostermayr1, S. Steinke1, E. A. Blakely1, Q. Ji1, A. Javey4, R. Kapadia5, C.G.R.

Geddes1, E. Esarey1

1Accelerator Technology and Applied Physics Division, Lawrence Berkeley National Laboratory, Berkeley,

CA 94720, USA

2 Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, CA

94720, USA

3Eurofins Materials Science Netherlands BV, 5656 AE Eindhoven, The Netherlands

4Electrical Engineering and Computer Science Department, University of California, Berkeley, CA 94720,

USA

5School of Engineering, University of Southern California, Los Angeles, CA 90089, USA

Corresponding author: T_Schenkel@LBL.gov

Nanostructured surfaces enhance ion yields in matrix assisted laser desorption-ionization mass

spectrometry (MALDI-MS). The spike protein complex, S1, is one fingerprint signature of Sars-CoV-2

with a mass of 75 kDa. Here, we show that MALDI-MS yields of Sars-CoV-2 spike protein ions in the 100

kDa range are enhanced 50-fold when the matrix-analyte solution is placed on substrates that are

coated with a dense forest of multi-walled carbon nanotubes, compared to yields from uncoated

substrates. Nanostructured substrates can support the development of mass spectrometry techniques

for sensitive pathogen detection and environmental monitoring.

The global SARS-CoV-2 pandemic since early 2020 has highlighted the need for low cost, sensitive,

robust and widely deployable techniques for detection of pathogens, such as the SARS-CoV-2 virus.

Mass spectrometry techniques are very widely used in bio-medical sciences. MALDI-MS (matrix-

assisted laser desorption/ionization mass spectrometry) is a relatively low cost and rapid technique [1].

In response to the current crisis, MALDI-MS based detection of SARS-CoV-2 signatures has been

reported from nasal swabs and from saliva samples [2-5]. In MALDI-MS, the use of (nano)-structured

substrates has been shown to enhance analyte ion yields and, in some cases, eliminate the need for a

matrix altogether [7-10]. However, these signal increases were limited to relatively low mass analyte

ions, below 10 kDa. Here, we report on the detection of SARS-CoV-2 spike protein (S1) ions in the 100

kDa mass range. The spike protein complex is a signature for detection of SARS-CoV-2 [2-4]. With a

mass of 75 kDa, direct detection in MALDI-MS is challenging as the desorption and ionization process in

the laser-matrix-analyte interaction can lead to fragmentation of the protein into a series of poly-

peptide and small fragment ions. This makes unique identification of pathogens difficult in MALDI-MS

experiments. Detection of robust signatures in mass spectra of SARS-CoV-2 samples is beneficial for the

development of environmental sensors and for rapid, low-cost testing capabilities outside laboratory

settings. We compare spike protein ion yields from carbon nanotube substrates to yields from standard

flat substrates (made from single crystal silicon wafers) for a series of MALDI-MS conditions and find S1

analyte ion yields that are enhanced 50-fold when we used carbon nanotube substrates.

Recombinant SARS-CoV-2 spike protein, S1, was purchased from R&D Systems (Minneapolis, MN,

USA). We prepared dilute solutions of S1 with sinapinic acid as a standard MALDI-MS matrix (purchased

from ProteoChem, Hurricane, UT, USA). The matrix analyte solution consisted of 10 mg of sinapinic

acid in a 1 ml of solution (50% acetonitrile and 50% water with 0.1% trifluoroacetic acid) and we

prepared analyte – matrix samples with 0.05 to 0.2 µg of S1 protein per 1 µl of matrix solution. We then

deposited drops of 2.5 µl of matrix-analyte solution onto flat silicon single crystal samples and onto

silicon samples which had been coated with a dense forest of multi-wall carbon nanotubes (CNT).

Aligned CNT were grown on silicon wafers in a plasma-enhanced chemical vapor deposition (PECVD)

process [11]. The growth process results in a relatively uniform height of CNT. A scanning electron

microscope (SEM) image of a sample with a CNT forest is shown in Figure 1 (a). The average diameter of

the CNTs is about 70 nm. In Figure 1 (b) we show a section of a dried drop of matrix-analyte solution

deposited on a CNT substrate. SEM images of mm-scale dried drops of matrix-analyte solution on CNT

and flat substrates are shown in Fig 1 (c, d, respectively). We observe formation of much denser

assemblies of matrix-analyte crystals on the CNT samples compared to flat substrates (silicon shown,

also titanium, not shown). The images (Fig 1, bottom row) also show damage spots from sample

exposure to laser pulses during MALDI-MS experiments.

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摘要：

1CarbonnanotubesubstratesenhanceSARS-CoV-2spikeproteinionyieldsinmatrixassistedlaserdesorption-ionizationmassspectrometryT.Schenkel1,A.M.Snijders2,K.Nakamura1,P.A.Seidl1,B.Mak1,L.Obst-Huebl1,H.Knobel3,I.Pong1,A.Persaud1,J.vanTilborg1,T.Ostermayr1,S.Steinke1,E.A.Blakely1,Q.Ji1,A.Javey4,R.Kapadia5,C.G...

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1 Carbon nanotube substrates enhance SARS -CoV-2 spike protein ion yields in matrix assisted laser desorption -ionization mass spectrometry

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