Team:IISc-Bangalore/Hardware/Results

Results

CALIBRATION:

Calibration of Version1.1 was done using KMnO4 and milk solutions of different dilutions. V1.1 can hold a test tube containing the sample and measure its optical density (OD). The same electronic circuitry was used to measure the OD values of the sample placed in a cuvette. The OD values of the sample was taken using a spectrophotometer (actual) and the device-V1.1 (measured).

KMnO4: Optical Density readings measured from a cuvette, using the device(V1.1) and a spectrophotometer.

Cuvette

Substance

Signal

OD(Actual)

OD(Measured)

Water

656

0

0

KMnO4 Dilutions

  

0.1

492

0.112

0.12

0.2

365

0.219

0.25

0.3

277

0.328

0.37

0.4

212

0.44

0.49

0.5

163

0.544

0.6

0.6

126

0.656

0.72

0.7

99

0.766

0.82

0.8

80

0.876

0.91

~0.9

64

0.999

1.01

~1

51

1.137

1.11












KMnO4: test tube readings

 

V1.1

Substance

Signal

OD(Actual)

OD(Measured)

Water

550

0

0

KMnO4 Dilutions

  

0.1

355

0.112

0.19

0.2

237

0.219

0.37

0.3

159

0.328

0.54

0.4

109

0.44

0.7

0.5

78

0.544

0.85

0.6

56

0.656

0.99

0.7

42

0.766

1.12

0.8

34

0.876

1.21

~0.9

27

0.999

1.31

~1

23

1.137

1.38






�

Milk: Cuvette readings

Cuvette

Substance

Signal

OD(Actual)

OD(Measured)

Water

627

0

0

Milk Dilutions

      

0.1

549

0.092

0.06

0.2

483

0.186

0.11

0.3

406

0.301

0.19

0.4

359

0.406

0.24

0.5

315

0.485

0.3

0.6

277

0.598

0.35

0.7

252

0.689

0.4

0.8

225

0.772

0.45

0.9

197

0.879

0.5

1.0

179

1.007

0.54




�

Milk: test tube (V1.1) readings

V1.1

Substance

Signal

OD(Actual)

OD(Measured)

Water

554

0

0

Milk Dilutions

      

0.1

452

0.092

0.09

0.2

375

0.186

0.17

0.3

299

0.301

0.27

0.4

244

0.406

0.36

0.5

206

0.485

0.43

0.6

168

0.598

0.52

0.7

143

0.689

0.59

0.8

122

0.772

0.66

0.9

102

0.879

0.73

1.0

83

1.007

0.82




















Growth Curves

 

Growth curves of Salmonella typhimurium (STMwt14028) and Escherichia coli were made. The optical densities were simultaneously measured using a spectrophotometer at wavelength 600nm and our device GCODe mini.

According to the Beer-Lambert’s law, we expect that the path length and epsilon to be different for our optical system as compared to the spectrophotometer. However, the concentration will still be the same in both cases. Hence, we expect the OD to be proportional.

Beer-Lambert’s Law: A=cl

where, A= Absorbance, = Absorbance, c=concentration, l=path length of the light

GCODe mini: Am=mclm

Spectrophotometer: As=scls

AmAs

In the following graphs, we have scaled the GCODe mini readings with the 12hr and the 24hr readings of the spectrophotometer.



�

 

24H Curve 1 STMwt14028

Time

(hours)

OD600 (Spectrophotometer)

V1 Reading

V1OD

OD600

V1OD_N_12H

V1OD_N_24H

0

0.0593

552

0.02

0.0122

0.009

0.009

3

0.2091

293

0.27

0.1121

0.124

0.115

6

0.3105

175

0.49

0.2135

0.226

0.209

9

0.3687

142

0.58

0.2717

0.267

0.247

12

0.4054

116

0.67

0.3084

0.308

0.286

24

0.4422

83

0.81

0.3452

0.373

0.345



�

 

24H Curve 2 STMwt14028

Time

(hours)

OD600 (Spectrophotometer)

V1 Reading

V1OD

OD600

V1OD_N_12H

V1OD_N_24H

0

0.0888

547.49

0.03

0.0392

0.017

0.016

3

0.2994

222.56

0.42

0.2498

0.236

0.22

6

0.3919

158.64

0.56

0.3423

0.315

0.293

9

0.4136

128.08

0.66

0.364

0.371

0.346

12

0.4711

104

0.75

0.4215

0.422

0.393

24

0.5579

63

0.97

0.5083

0.545

0.508



�

 

24H Curve 1 E.coli

Time

(hours)

OD600 (Spectrophotometer)

V1 Reading

V1OD

OD600

V1OD_N_12H

V1OD_N_10H

0

0.118

584.04

0

0

0

0

2

0.173

511.48

0.06

0.055

0.1

0.101

4

0.437

354.87

0.22

0.319

0.367

0.369

6

0.633

278.55

0.32

0.515

0.534

0.536

8

0.706

246.26

0.38

0.588

0.634

0.637

10

0.805

225.58

0.41

0.687

0.684

0.687

12

0.869

207.19

0.45

0.751

0.751

0.754

24.5

1.194

165.33

0.55

1.076

0.918

0.922

 

�

 

24H Curve 2 E.coli

Time

(hours)

OD600 (Spectrophotometer)

V1 Reading

V1OD

OD600

V1OD_N_12H

V1OD_N_10H

0

0.111

595.4

0

0

0

0

2

0.183

512.38

0.07

0.072

0.117

0.11

4

0.444

345.93

0.24

0.333

0.399

0.378

6

0.66

286.98

0.32

0.549

0.533

0.504

8

0.687

252.75

0.37

0.576

0.616

0.582

10

0.772

226.86

0.42

0.661

0.699

0.661

12

0.86

210.33

0.45

0.749

0.749

0.708

24.5

1.106

174.59

0.53

0.995

0.882

0.834



Notice that the readings from the Mini form an even smoother curve than those from the spectrophotometer! This is probably because the GCODe readings were taken instantaneously, while it takes time to load the cuvette into the spectrophotometer and take a reading, allowing lots more opportunities for human error.